**UNITED
      STATES**


**SECURITIES
      AND EXCHANGE COMMISSION**


**Washington,
      D.C. 20549**








**FORM
      10-K**








**[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 AND
      EXCHANGE ACT OF 1934**





For
      the
      transition period from ________to _______





Commission
      file number 333-120575-12





**STRUCTURED
      ASSET SECURITIES CORPORATION**


(Exact
      name of registrant as specified in its charter)





Delaware
            
            74-2440850(State
                or other jurisdiction of
              incorporation
                or organization)
            
            (I.R.S.
                Employer
              Identification
                No.)





745
      Seventh Avenue, 7 th Floor, New York, New York 10019


(Address
      of principal executive offices)





Registrant’s
      telephone number, including area code: 212-526-7000


Structured
        Asset Securities Corporation Mortgage Pass-Through Certificates, Series
        2005-4XS
 (Exact
        name of issuing entity as specified in its charter)
  Lehman
        Brothers Holdings Inc.
 (Exact
        name of sponsor as specified in its charter)


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





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.





oYes
            
            xNo





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





oYes
            
            xNo





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.





xYes
            
            oNo





Indicate
      by check mark if disclosure of delinquent filers pursuant to Item 405 of
      Regulation S K (~229.405 of this chapter) 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.





Not
      Applicable





Indicate
      by check mark whether the registrant is a large accelerated filer, an
      accelerated filer, or a non-accelerated filer. See definition of “accelerated
      filer and large accelerated filer” in Rule 12b-2 of the Exchange Act (Check
      one):





Large
                accelerated filero
            
            
            Accelerated
                filero
            
            
            Non-accelerated
                filerx








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





oYes
            
            xNo








State
      the
      aggregate market value of the voting and non voting common equity held by
      non-affiliates computed by reference to the price at which the common equity
      was
      last sold, or the average bid and asked price of such common equity, as of
      the
      last business day of the registrant’s most recently completed second fiscal
      quarter.





Not
      Applicable








DOCUMENTS
      INCORPORATED BY REFERENCE





Not
      Applicable








**PART
      I**





**Item
      1. Business.**





Not
      applicable.





**Item
      1A. Risk Factors.**





Not
      applicable.





**Item
      1B. Unresolved Staff Comments.**





Not
      applicable.





**Item
      2. Properties.**





Not
      applicable.





**Item
      3. Legal Proceedings.**





The
      registrant knows of no material pending legal proceedings involving the trust
      created under the Trust Agreement for the Structured Asset Securities
      Corporation Mortgage Pass-Through Certificates, Series 2005-4XS (the “Trust”),
      the Trustee, the Master Servicer or the registrant with respect to the Trust
      other than routine litigation incidental to the duties of the respective
      parties.





**Item
      4. Submission of Matters to a Vote of Security Holders.**





None.








**PART
      II**





**Item
      5. Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer
      Purchases of Equity Securities.**





No
      established public trading market for the Certificates exists.


Records
      provided to the Trust by the DTC and the Trustee indicate that as of December
      31, 2005, the total number of holders of record for the Series of Certificates
      is 71.





**Item
      6. Selected Financial Data.**





Not
      applicable.





**Item
      7. Management’s Discussion and Analysis of Financial Condition and Results of
      Operation.**





Not
      applicable.





**Item
      7A. Quantitative and Qualitative Disclosures About Market
      Risk.**





Not
      applicable.





**Item
      8. Financial Statements and Supplementary Data.**





Not
      applicable.





**Item
      9. Changes in and Disagreements With Accountants on Accounting and Financial
      Disclosure.**





Not
      applicable.





**Item
      9A. Controls and Procedures.**





Not
      applicable.





**Item
      9B. Other Information.**





None.








**PART
      III**





**Item
      10. Directors and Executive Officers of the Registrant.**





Not
      applicable.





**Item
      11. Executive Compensation.**





Not
      applicable.





**Item
      12. Security Ownership of Certain Beneficial Owners and Management and Related
      Stockholder Matters.**





Not
      applicable.





**Item
      13. Certain Relationships and Related Transactions.**





Not
      applicable.





**Item
      14. Principal Accounting Fees and Services.**





Not
      applicable.








**PART
      IV**








**Item
      15. Exhibits, Financial Statement Schedules.**





Exhibits





The
      exhibits required to be filed by Registrant pursuant to Item 601 of Regulation
      S-K are listed in the Exhibit Index below:





**EXHIBIT
      INDEX**


**Exhibit
                Number**
            **Description**31
            Sarbanes-Oxley
                Certification99.1(a)
            Annual
                Independent Accountants’ Report,Aurora
                Loan Services LLC, as Servicer (Year ended November 30,
                2005)99.1(b)
            Annual
                Independent Accountants’ Report, ABN AMRO Mortgage Group, Inc., as
                Servicer99.1(c)
            Annual
                Independent Accountants’ Report, Bank of America, N.A., as
                Servicer99.1(d)
            Annual
                Independent Accountants’ Report, Chase Home Finance LLC, as
                Servicer99.1(e)
            Annual
                Independent Accountants’ Report, CitiMortgage, Inc., as
                Servicer99.1(f)
            Annual
                Independent Accountants’ Report, Colonial Savings, F.A., as Servicer (Year
                ended September 30, 2005)99.1(g)
            Annual
                Independent Accountants’ Report, GMAC Mortgage Corporation, as
                Servicer99.1(h)
            Annual
                Independent Accountants’ Report, National City Mortgage Company, as
                Servicer99.1(i)
            Annual
                Independent Accountants’ Report, Wachovia Mortgage Corporation, as
                Servicer99.1(j)
            Annual
                Independent Accountants’ Report, Wells Fargo Bank, NA, as
                Servicer99.2(a)
            Report
                of Management, Aurora Loan Services LLC, as Servicer (Year ended
                November
                30, 2005)99.2(b)
            Report
                of Management, ABN AMRO Mortgage Group, Inc., as
                Servicer99.2(c)
            Report
                of Management, Bank of America, N.A., as Servicer99.2(d)
            Report
                of Management, Chase Home Finance LLC, as Servicer99.2(e)
            Report
                of Management, CitiMortgage, Inc., as Servicer99.2(f)
            Report
                of Management, Colonial Savings, F.A., as Servicer (Year ended September
                30, 2005)99.2(g)
            Report
                of Management, GMAC Mortgage Corporation, as Servicer99.2(h)
            Report
                of Management, National City Mortgage Company, as
                Servicer99.2(i)
            Report
                of Management, Wachovia Mortgage Corporation, as
                Servicer99.2(j)
            Report
                of Management, Wells Fargo Bank, NA, as Servicer99.3
            Annual
                Statement of Compliance, Aurora Loan Services LLC, as Master
                Servicer











**SIGNATURES**





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.





Structured
      Asset Securities Corporation


(Registrant)





By: /s/
        E.Todd Whittemore
 E.
        Todd
        Whittemore, Executive Vice President
 Aurora
        Loan Services LLC, as Master Servicer
 
 Date:
        March 29, 2006