SC 13D/A

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934
(Amendment No. 29 )*

NATIONAL PROPERTY INVESTORS 4

(Name of Issuer)

Limited Partnership Units

(Title of Class of Securities)

None

(CUSIP Number)

John Bezzant
Executive Vice President
Apartment Investment and Management Company
4582 South Ulster Street Parkway, Suite 1100
Denver, Colorado 80237
(303) 757-8101

with a copy to:
Robert Mintz, Esq.
Hogan Lovells US LLP
One Tabor Center
1200 Seventeenth St., Suite 1500
Denver, Colorado 80202
(303) 899-7300

(Name, Address and Telephone Number of Person Authorized to
Receive Notices and Communications)

July 26, 2011

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. o

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

* The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. Not Applicable  Page 2  of  10 

1	NAMES OF REPORTING PERSONS AIMCO Properties, L.P. I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (entities only) 84-1275721
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
	(a)   o
	(b)   þ
3	SEC USE ONLY
4	SOURCE OF FUNDS
	WC
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)
	o
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	Delaware
		7	SOLE VOTING POWER
NUMBER OF
SHARES		8	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			47,850 Units
EACH		9	SOLE DISPOSITIVE POWER
REPORTING
PERSON
WITH		10	SHARED DISPOSITIVE POWER
			47,850 Units
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	47,850 Units
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)
	o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	79.74%
14	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
	PN

CUSIP No. Not Applicable  Page 3  of  10 

1	NAMES OF REPORTING PERSONS AIMCO-GP, INC. I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (entities only)
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
	(a)   o
	(b)   þ
3	SEC USE ONLY
4	SOURCE OF FUNDS
	WC
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)
	o
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	Delaware
		7	SOLE VOTING POWER
NUMBER OF
SHARES		8	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			47,850 Units
EACH		9	SOLE DISPOSITIVE POWER
REPORTING
PERSON
WITH		10	SHARED DISPOSITIVE POWER
			47,850 Units
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	47,850 Units
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)
	o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	79.74%
14	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
	CO

CUSIP No. Not Applicable  Page 4  of  10 

1	NAMES OF REPORTING PERSONS APARTMENT INVESTMENT AND MANAGEMENT COMPANY I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (entities only) 84-1259577
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
	(a)   o
	(b)   þ
3	SEC USE ONLY
4	SOURCE OF FUNDS
	WC
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)
	o
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	Maryland
		7	SOLE VOTING POWER
NUMBER OF
SHARES		8	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			47,850 Units
EACH		9	SOLE DISPOSITIVE POWER
REPORTING
PERSON
WITH		10	SHARED DISPOSITIVE POWER
			47,850 Units
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	47,850 Units
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)
	o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	79.74%
14	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
	CO

CUSIP No. Not Applicable  Page 5  of  10 

1	NAMES OF REPORTING PERSONS AIMCO IPLP, L.P. I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (entities only)
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
	(a)   o
	(b)   þ
3	SEC USE ONLY
4	SOURCE OF FUNDS
	WC
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)
	o
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	Delaware
		7	SOLE VOTING POWER
NUMBER OF
SHARES		8	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			36,977 Units
EACH		9	SOLE DISPOSITIVE POWER
REPORTING
PERSON
WITH		10	SHARED DISPOSITIVE POWER
			36,977 Units
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	36,977 Units
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)
	o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	61.62%
14	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
	PN

CUSIP No. Not Applicable  Page 6  of  10 

1	NAMES OF REPORTING PERSONS AIMCO/IPT, INC. I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (entities only)
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
	(a)   o
	(b)   þ
3	SEC USE ONLY
4	SOURCE OF FUNDS
	WC
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)
	o
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	Delaware
		7	SOLE VOTING POWER
NUMBER OF
SHARES		8	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			36,977 Units
EACH		9	SOLE DISPOSITIVE POWER
REPORTING
PERSON
WITH		10	SHARED DISPOSITIVE POWER
			36,977 Units
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	36,977 Units
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)
	o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	61.62%
14	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
	CO

CUSIP No. Not Applicable  Page 7  of  10 

1	NAMES OF REPORTING PERSONS IPLP ACQUISITIONS I, L.L.C. I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (entities only)
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
	(a)   o
	(b)   þ
3	SEC USE ONLY
4	SOURCE OF FUNDS
	WC
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)
	o
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	Delaware
		7	SOLE VOTING POWER
NUMBER OF
SHARES		8	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			4,452 Units
EACH		9	SOLE DISPOSITIVE POWER
REPORTING
PERSON
WITH		10	SHARED DISPOSITIVE POWER
			4,452 Units
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	4,452 Units
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)
	o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	7.42%
14	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
	OO

CUSIP No. Not Applicable  Page 8  of  10 

Introductory Note

     This Amendment No. 29 (this “Amendment No. 29”) is filed with respect to the issuer, National Property Investors 4, a California limited partnership (the “Partnership”), by AIMCO Properties, L.P. (“AIMCO Properties”), AIMCO-GP, Inc. (“AIMCO-GP”), Apartment Investment and Management Company (“AIMCO”), AIMCO IPLP, L.P. (“AIMCO IPLP”), AIMCO/IPT, INC. (“AIMCO/IPT”) and IPLP Acquisitions I, L.L.C. (“IPLP Acquisitions” and, together with AIMCO Properties, AIMCO-GP, AIMCO, AIMCO IPLP, and AIMCO/IPT, the “Reporting Persons”). This Amendment No. 29 amends and supplements the statement on Schedule 13D, as amended and supplemented to date (the “Schedule 13D”), previously filed with the Securities and Exchange Commission with respect to the Partnership by the Reporting Persons or certain of their affiliates.

     The Schedule 13D is amended to make the following changes to Items 4 and 5:

Item 4. Purpose of Transaction

     Item 4 is hereby supplemented by the addition of the following information:

     The Reporting Persons, which are all affiliates of NPI Equity Investments, Inc., the general partner of the Partnership (the “General Partner”), have reviewed their investment in the Partnership in light of numerous factors, including, without limitation, general market and economic conditions, their on-going analysis of the Partnership’s business, financial condition, operations and prospects, and the relative attractiveness of alternative investment opportunities and other future developments. As part of this review, the General Partner and AIMCO Properties are considering a merger transaction in which AIMCO Properties would acquire 100% ownership of the Partnership. The transaction, if consummated, would result in the Partnership’s equity securities becoming eligible for termination of registration pursuant to Section 12(g)(4) of the Securities Exchange Act of 1934, as amended.

     The terms of the above-described transaction are still being considered, and either AIMCO Properties or the General Partner may decide not to pursue the transaction, or to pursue a different transaction. Although the foregoing reflects potential activities presently contemplated by the Reporting Persons with respect to the Partnership, the foregoing is subject to change at any time, and there can be no assurance that the Reporting Persons will take any of the actions referred to above or participate in a group that will take any of the actions referred to above.

Item 5. Interest in Securities of the Issuer

     Item 5 is hereby amended and restated in its entirety as follows:

     (a)-(b) The information in lines 7 through 11 and 13 of each Reporting Person’s cover page is incorporated herein by reference.

CUSIP No. Not Applicable  Page 9  of  10 

Item 7. Material to Be Filed as Exhibits

The following is filed herewith as an Exhibit to this Statement:

     Exhibit 7.1 Agreement of Joint Filing, dated July 26, 2011

CUSIP No. Not Applicable  Page 10  of  10 

SIGNATURE

     After reasonable inquiry and to the best of our knowledge and belief, the undersigned certify that the information set forth in this statement is true, complete and correct.

Dated: July 26, 2011
	AIMCO PROPERTIES, L.P.
	By:	AIMCO-GP, INC.
		(General Partner)
	AIMCO-GP, INC. APARTMENT INVESTMENT AND MANAGEMENT COMPANY AIMCO IPLP, L.P.
	By:	AIMCO-GP, INC.
		(General Partner)
	AIMCO/IPT INC. IPLP ACQUISITIONS I, L.L.C.
	By:	/s/ Trent A. Johnson
		Name:	Trent A. Johnson
		Title:	Authorized Signatory

EX-7.1

EXHIBIT 7.1

AGREEMENT OF JOINT FILING

     The parties listed below agree that the Amendment No. 29 to Schedule 13D to which this agreement is attached as an exhibit, and all further amendments thereto, shall be filed on behalf of each of them. This Agreement is intended to satisfy Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended. This Agreement may be executed in any number of counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument.

Dated: July 26, 2011

AIMCO PROPERTIES, L.P.
By:	AIMCO-GP, INC.
	(General Partner)
AIMCO-GP, INC. APARTMENT INVESTMENT AND MANAGEMENT COMPANY AIMCO IPLP, L.P.
By:	AIMCO-GP, INC.
	(General Partner)
AIMCO/IPT INC. IPLP ACQUISITIONS I, L.L.C.
By:	/s/ Trent A. Johnson
	Name:	Trent A. Johnson
	Title:	Authorized Signatory