SEC Registration Nos.

Nos. 811-09877 and 333-34122

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933
Post-Effective Amendment No. 23	x

and/or

REGISTRATION STATEMENT

UNDER

THE INVESTMENT ACT OF 1940
Amendment No. 25	x

Calvert Social Index Series, Inc.

(Exact Name of Registrant as Specified in Charter)

4550 Montgomery Avenue

Bethesda, Maryland 20814

(Address of Principal Executive Offices)

Registrant’s Telephone Number: (301) 951-4800

William M. Tartikoff

4550 Montgomery Avenue

Bethesda, Maryland 20814

(Name and Address of Agent for Service)

It is proposed that this filing will become effective (check appropriate box):

x immediately upon filing pursuant to paragraph (b)

¨ on (date) pursuant to paragraph (b)

¨ 60 days after filing pursuant to paragraph (a)(1)

¨ on (date) pursuant to paragraph (a)(1)

¨ 75 days after filing pursuant to paragraph (a)(2)

¨ on (date) pursuant to paragraph (a)(2) of Rule 485.

EXPLANATORY NOTE

This Post-Effective Amendment is being filed solely to submit exhibits containing risk/return summary information in interactive data format that is identical to the risk/return information filed as part of the Post-Effective Amendment No. 22 to this Registration Statement, as filed on January 30, 2013.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for effectiveness of this registration statement under Rule 485(b) under the Securities Act and has duly caused this registration statement to be signed on its behalf by the undersigned, duly authorized, in the City of Bethesda, and State of Maryland on the 7th day of February 2013.

CALVERT SOCIAL INDEX SERIES, INC.

BY:

                **             

Barbara Krumsiek

Senior Vice President and Director

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed below on the 7th day of February 2013, by the following persons in the capacities indicated.

Signature	Title
**	PRESIDENT AND DIRECTOR
D. WAYNE SILBY
**	DIRECTOR
JOHN G. GUFFEY, JR.
**	SENIOR VICE PRESIDENT AND DIRECTOR
BARBARA J. KRUMSIEK
**	PRINCIPAL ACCOUNTING OFFICER
RONALD M. WOLFSHEIMER
**	DIRECTOR
REBECCA L. ADAMSON
**	DIRECTOR
RICHARD L. BAIRD, JR.
**	DIRECTOR
JOY V. JONES
**	DIRECTOR
TERRENCE J. MOLLNER
**	DIRECTOR
SYDNEY A. MORRIS
**	DIRECTOR
MILES D. HARPER, III
**By: /s/ Lancelot A. King
Lancelot A. King

Executed by Lancelot A. King, Attorney-in-fact on behalf of those indicated, pursuant to Power of Attorney Forms, incorporated by reference to Registrant’s Post-Effective Amendment No. 22, January 30, 2013, Accession Number 0001105446-13-000001.

Calvert Social Index Series, Inc.

Post-Effective Amendment No. 23

Registration No. 333-34122

EXHIBIT INDEX

XBRL Instance Document	Ex-101.ins
XBRL Taxonomy Extension Schema Document	Ex-101.sch
XBRL Taxonomy Extension Labels Linkbase	Ex-101.lab
XBRL Taxonomy Extension Presentation Linkbase Document	Ex-101.pre
XBRL Taxonomy Extension Definition Linkbase	Ex-101.def
XBRL Taxonomy Extension Calculation Linkbase	Ex-101.cal