Exhibit 31.1

Sarbanes - Oxley Section 302 Certification

I, Thomas J. May, certify that:



|1. | I have reviewed this annual report on Form 10-K of NSTAR;
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|2. | Based on my knowledge, this annual report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light
of the circumstances under which such statements were made, not misleading with respect to the period covered by this annual report;
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|3. | Based on my knowledge, the financial statements, and other financial information included in this annual report, fairly present in all material respects the financial condition,
results of operations and cash flows of NSTAR as of, and for, the periods presented in this annual report;
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|4. | NSTARs other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and
15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for NSTAR and have:
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| | a) | designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information
relating to NSTAR, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this annual report is being prepared;
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| | b) | designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable
assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;
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| | c) | evaluated the effectiveness of NSTARs disclosure controls and procedures and presented in this annual report our conclusions about the effectiveness of the disclosure controls
and procedures, as of the end of the period covered by this annual report, based on such evaluation; and
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| | d) | disclosed in this annual report any change in NSTARs internal control over financial reporting that occurred during NSTARs most recent fiscal quarter that has materially
affected, or is reasonably likely to materially affect, NSTARs internal control over financial reporting; and
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|5. | NSTARs other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to NSTARs auditors and the audit
committee of NSTARs board of trustees:
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| | a) | all significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect
NSTARs ability to record, process, summarize and report financial information; and
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| | b) | any fraud, whether or not material, that involves management or other employees who have a significant role in NSTARs internal control over financial reporting.
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|                        |  |  |  |                                                
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|Date: February 16, 2007 |  |  |  | /s/ THOMAS J. MAY                              
|                        |  |  |  | Thomas J. May                                  
|                        |  |  |  | Chairman, President and Chief Executive Officer