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UNITED STATES SECURITIES AND

EXCHANGE COMMISSION

Washington, D.C. 20549



FORM 10-K/A

Amendment No. 1



|x | ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
|- | ------------------------------------------------------------------------------------



For the fiscal year ended December 31, 2005



or



| ̈ | TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
|- | ----------------------------------------------------------------------------------------



For the transition period from
                     to



Commission file number 1-14768



NSTAR

(Exact name of registrant as specified in its charter)



|                                                               |  |                                        
|-------------------------------------------------------------- |  | ---------------------------------------
|Massachusetts                                                  |  | 04-3466300                             
|(State or other jurisdiction of incorporation or organization) |  | (I.R.S. Employer Identification Number)
|                                                               | 
|800 Boylston Street, Boston, Massachusetts                     |  | 02199                                  
|(Address of principal executive offices)                       |  | (Zip code)                             



617 424-2000

(Registrants telephone number, including area code)



Securities registered pursuant to Section 12(b) of the Act:



|                                      |  |                                              
|------------------------------------- |  | ---------------------------------------------
|Title of each class                   |  | Name of each exchange on which registered    
|Common Shares, Par Value $1 per share |  | New York Stock Exchange Boston Stock Exchange



Securities
registered pursuant to Section 12(g) of the Act: None



Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.



x  Yes ̈No



Indicate by
check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.



 ̈Yes    x  No



Indicate by
check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to
file such reports), and (2) has been subject to such filing requirements for the past 90 days.



x  Yes ̈No



Indicate by check mark if disclosure of delinquent filers
pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrants knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any
amendment to this Form 10-K.  x



Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, or a non-accelerated filer, as defined in Rule 12b-2 of the Exchange Act.



Large accelerated filer  x            Accelerated filer ̈Non-accelerated filer ̈



Indicate by check mark whether the registrant is a shell company (as defined
in Rule 12b-2 of the Act)



 ̈Yes    x  No



The aggregate market value of the 106,808,376 shares of voting stock of the registrant held by non-affiliates of the
registrant, computed as the average of the high and low market prices of the common shares as reported on the New York Stock Exchange consolidated transaction reporting system for NSTAR Common Shares as of the last business day of the
registrants most recently completed second fiscal quarter: $3,291,834,148.



Indicate the number of shares outstanding of each of the registrants classes of common stock, as of the latest practicable date:



|                            |  |                                 
|--------------------------- |  | --------------------------------
|Class                       |  | Outstanding at February 17, 2006
|Common Shares, $1 par value |  | 106,808,376 Shares              



Documents
Incorporated by Reference



Sections of NSTARs Definitive Proxy
Statement for the 2006 Annual Meeting of Shareholders to be held on May 4, 2006 are incorporated by reference into Parts I and III of this Form 10-K.



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##### Table of Contents

NSTAR



Form 10-K/A

Amendment No. 1



Table of Contents



|                                                                   |  |     
|------------------------------------------------------------------ |  | ----
|                                                                   |  | Page
|Explanatory Note                                                   |  | 2   
|                                                                   | 
|Item 8. Financial Statements and Supplementary Data                |  |     
|Consolidated Balance Sheets (replaces page 51 in original filing) |  | 3   
|                                                                   | 
|Item 15. Exhibits and Financial Statement Schedules                |  | 4   
|                                                                   | 
|Signature                                                          |  | 5   
|                                                                   | 
|Exhibit 31Rule 13a  15/15d-15(e) Certifications                  |  |     
|                                                                   | 
|Exhibit 32Section 1350 Certifications                             |  |     



1



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##### Table of Contents

Explanatory Note



This Amendment
No. 1 to NSTARs Annual Report on Form 10-K for the fiscal year ended December 31, 2005 (the Annual Report) is being filed solely to amend a single amount on the Consolidated Balance Sheets reflecting the Utility plant in
service, at original cost, at December 31, 2005 included in Item 8. As a result of a typographical error by NSTARs printer/filing agent made in the process of converting and formatting the Annual Report to an electronic format suitable
for filing with the Commission, the EDGAR version of the Form 10-K reflected an incorrect amount for Utility plant in service, at original cost, for 2005 and was filed in the original Form 10-K on February 17, 2006 as $4,454,774 (in thousands).
The correct amount should have been $4,671,059 (in thousands). The detailed description of Utility Plant included in the original filing in Note A. Business Organization and Summary of Significant Accounting Policies, reflects the
correct amount.



Except as described above, no other changes or
amendments have been made to the Annual Report as previously filed for changes in events, estimates or other developments subsequent to February 17, 2006, the date of the original filing of the Annual Report. For a discussion of any potential
subsequent events and developments that may be material to investors, please refer to the NSTARs filings with the Securities and Exchange Commission subsequent to February 17, 2006.



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##### Table of Contents

Item 8.    Financial Statements and Supplementary Data



NSTAR

Consolidated Balance Sheets



|                                                                                                                                                       |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|------------------------------------------------------------------------------------------------------------------------------------------------------ |  | -------------- | --------- | ---- |  | - | --------- |  | - | --------- | - |  | - | ---------
|                                                                                                                                                       |  | December 31,  
|                                                                                                                                                       |  | 2005           |           | 2004
|Assets                                                                                                                                                 |  | (in thousands)
|Utility plant in service, at original cost                                                                                                             |  | $              | 4,671,059 |      |  |   |           |  | $ | 4,454,774 |   |  |   |          
|Less: accumulated depreciation                                                                                                                         |  |                | 1,178,259 |      |  |   | 3,492,800 |  |   | 1,122,810 |   |  |   | 3,331,964
|                                                                                                                                                       |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Construction work in progress                                                                                                                          |  |                |           |      |  |   | 208,957   |  |   |           |   |  |   | 103,866  
|                                                                                                                                                       |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Net utility plant                                                                                                                                      |  |                |           |      |  |   | 3,701,757 |  |   |           |   |  |   | 3,435,830
|Non-utility property, net                                                                                                                              |  |                |           |      |  |   | 138,222   |  |   |           |   |  |   | 144,148  
|Equity investments                                                                                                                                     |  |                |           |      |  |   | 13,705    |  |   |           |   |  |   | 13,887   
|Other investments                                                                                                                                      |  |                |           |      |  |   | 63,441    |  |   |           |   |  |   | 59,096   
|Current assets:                                                                                                                                        |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Cash and cash equivalents                                                                                                                              |  |                | 15,612    |      |  |   |           |  |   | 12,497    |   |  |   |          
|Restricted cash                                                                                                                                        |  |                | 14,282    |      |  |   |           |  |   | 10,254    |   |  |   |          
|Accounts receivable, net of allowance of $24,504 and $21,804, respectively                                                                             |  |                | 305,441   |      |  |   |           |  |   | 302,194   |   |  |   |          
|Accrued unbilled revenues                                                                                                                              |  |                | 59,400    |      |  |   |           |  |   | 53,752    |   |  |   |          
|Regulatory assets                                                                                                                                      |  |                | 446,286   |      |  |   |           |  |   | 300,238   |   |  |   |          
|Inventory, at average cost                                                                                                                             |  |                | 120,924   |      |  |   |           |  |   | 86,397    |   |  |   |          
|Income taxes                                                                                                                                           |  |                | 57,444    |      |  |   |           |  |   | 21,063    |   |  |   |          
|Other                                                                                                                                                  |  |                | 16,894    |      |  |   | 1,036,283 |  |   | 11,434    |   |  |   | 797,829  
|                                                                                                                                                       |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Deferred debits:                                                                                                                                       |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Regulatory assets - energy contracts                                                                                                                   |  |                |           |      |  |   | 683,193   |  |   |           |   |  |   | 1,269,651
|Regulatory asset - goodwill                                                                                                                            |  |                |           |      |  |   | 658,538   |  |   |           |   |  |   | 678,698  
|Regulatory assets - other                                                                                                                              |  |                |           |      |  |   | 924,693   |  |   |           |   |  |   | 607,037  
|Prepaid pension                                                                                                                                        |  |                |           |      |  |   | 346,889   |  |   |           |   |  |   | 297,746  
|Other                                                                                                                                                  |  |                |           |      |  |   | 78,843    |  |   |           |   |  |   | 87,434   
|                                                                                                                                                       |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Total assets                                                                                                                                           |  |                |           |      |  | $ | 7,645,564 |  |   |           |   |  | $ | 7,391,356
|                                                                                                                                                       |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Capitalization and Liabilities                                                                                                                         |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Common equity:                                                                                                                                         |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Common shares, par value $1 per share, 200,000,000 shares authorized; 106,808,376 shares in 2005 and 106,550,282 shares in 2004 issued and
outstanding |  | $              | 106,808   |      |  |   |           |  | $ | 106,550   |   |  |   |          
|Premium on common shares                                                                                                                               |  |                | 813,099   |      |  |   |           |  |   | 819,454   |   |  |   |          
|Retained earnings                                                                                                                                      |  |                | 621,500   |      |  |   |           |  |   | 518,252   |   |  |   |          
|Accumulated other comprehensive loss                                                                                                                   |  |                | (6,392    | )    |  |   | 1,535,015 |  |   | (3,374    | ) |  |   | 1,440,882
|                                                                                                                                                       |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Cumulative non-mandatory redeemable preferred stock of subsidiary                                                                                      |  |                |           |      |  |   | 43,000    |  |   |           |   |  |   | 43,000   
|Long-term debt                                                                                                                                         |  |                |           |      |  |   | 1,614,411 |  |   |           |   |  |   | 1,792,654
|Transition property securitization                                                                                                                     |  |                |           |      |  |   | 787,966   |  |   |           |   |  |   | 308,748  
|Current liabilities:                                                                                                                                   |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Long-term debt                                                                                                                                         |  |                | 28,457    |      |  |   |           |  |   | 108,197   |   |  |   |          
|Transition property securitization                                                                                                                     |  |                | 94,683    |      |  |   |           |  |   | 41,048    |   |  |   |          
|Notes payable                                                                                                                                          |  |                | 417,500   |      |  |   |           |  |   | 161,400   |   |  |   |          
|Deferred income taxes                                                                                                                                  |  |                | 7,232     |      |  |   |           |  |   | 8,072     |   |  |   |          
|Accounts payable                                                                                                                                       |  |                | 320,960   |      |  |   |           |  |   | 239,613   |   |  |   |          
|Energy contracts                                                                                                                                       |  |                | 183,674   |      |  |   |           |  |   | 171,312   |   |  |   |          
|Accrued interest                                                                                                                                       |  |                | 33,114    |      |  |   |           |  |   | 33,073    |   |  |   |          
|Dividends payable                                                                                                                                      |  |                | 327       |      |  |   |           |  |   | 31,227    |   |  |   |          
|Accrued expenses                                                                                                                                       |  |                | 20,729    |      |  |   |           |  |   | 30,654    |   |  |   |          
|Other                                                                                                                                                  |  |                | 62,769    |      |  |   | 1,169,445 |  |   | 73,346    |   |  |   | 897,942  
|                                                                                                                                                       |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Deferred credits:                                                                                                                                      |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Accumulated deferred income taxes and unamortized investment tax credits                                                                               |  |                |           |      |  |   | 1,273,456 |  |   |           |   |  |   | 1,114,588
|Energy contracts                                                                                                                                       |  |                |           |      |  |   | 683,193   |  |   |           |   |  |   | 1,269,651
|Pension liability                                                                                                                                      |  |                |           |      |  |   | 37,351    |  |   |           |   |  |   | 31,296   
|Regulatory liability - cost of removal                                                                                                                 |  |                |           |      |  |   | 258,782   |  |   |           |   |  |   | 258,722  
|Other                                                                                                                                                  |  |                |           |      |  |   | 242,945   |  |   |           |   |  |   | 233,873  
|Commitments and contingencies                                                                                                                          |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|                                                                                                                                                       |  |                |           |      |  |   |           |  |   |           |   |  |   |          
|Total capitalization and liabilities                                                                                                                   |  |                |           |      |  | $ | 7,645,564 |  |   |           |   |  | $ | 7,391,356
|                                                                                                                                                       |  |                |           |      |  |   |           |  |   |           |   |  |   |          



The accompanying notes
are an integral part of the consolidated financial statements.



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|Item 15. | Exhibits and Financial Statement Schedules
|-------- | ------------------------------------------



NSTAR and its subsidiaries



|           |  |                                                                                                                      
|---------- |  | ---------------------------------------------------------------------------------------------------------------------
|           | 
|Exhibit 31 |  | Rule 13a - 15/15d-15(e) Certifications (filed herewith)                                                              
|31.1       |  | Certification Statement of Chief Executive Officer of NSTAR pursuant to Section 302 of the Sarbanes-Oxley Act of 2002
|           | 
|31.2       |  | Certification Statement of Chief Financial Officer of NSTAR pursuant to Section 302 of the Sarbanes-Oxley Act of 2002
|           | 
|Exhibit 32 |  | Section 1350 Certifications (filed herewith)                                                                         
|32.1       |  | Certification Statement of Chief Executive Officer of NSTAR pursuant to Section 906 of the Sarbanes-Oxley Act of 2002
|           | 
|32.2       |  | Certification Statement of Chief Financial Officer of NSTAR pursuant to Section 906 of the Sarbanes-Oxley Act of 2002



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|            |  |       |  |                  
|----------- |  | ----- |  | -----------------
|FORM 10-K/A |  | NSTAR |  | DECEMBER 31, 2005



SIGNATURE



Pursuant to the
requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.



| |  |                         |  |  |  |              |  |                               
| |  | ----------------------- |  |  |  | ------------ |  | ------------------------------
| |  |                         |  |  |  | NSTAR       
| |  |                         |  |  |  | (Registrant)
| |  |                         |  | 
| |  | Date: February 27, 2006 |  |  |  | By:          |  | /s/    ROBERT J. WEAFER,
JR.  
| |  |                         |  |  |  |              |  | Robert J. Weafer, Jr.         
| |  |                         |  |  |  |              |  | Vice President, Controller and
| |  |                         |  |  |  |              |  | Chief Accounting Officer      



5