As filed with the Securities and Exchange Commission on May 15, 2020

Securities Act Registration No. 2-34223

Investment Company Act File No. 811-1829

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Post-Effective Amendment No. 113

and

REGISTRATION STATEMENT

UNDER

THE INVESTMENT COMPANY ACT OF 1940

Amendment No. 88

COLUMBIA ACORN TRUST

71 S. Wacker Drive, Suite 2500

Chicago, IL 60606

Telephone number: 312.634.9200

Ryan C. Larrenaga c/o Columbia Management Investment Advisers, LLC 225 Franklin Street Boston, MA 02110	Matthew A. Litfin Louis J. Mendes Columbia Acorn Trust 71 S. Wacker Drive Suite 2500 Chicago, IL 60606	Mary C. Moynihan Perkins Coie LLP 700 13th Street, N.W., Suite 800 Washington, D.C. 20005
(Agents for service)

It is proposed that this filing will become effective:

☒ immediately upon filing pursuant to rule 485(b)

☐ on (date) pursuant to rule 485(b)

☐ 60 days after filing pursuant to rule 485(a)(1)

☐ on                      pursuant to rule 485(a)(l)

☐ 75 days after filing pursuant to rule 485(a)(2)

☐ on                      pursuant to rule 485(a)(2).

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 the requirements for effectiveness of this post-effective amendment pursuant to Rule 485(b) under the Securities Act of 1933 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Chicago and State of Illinois on May 15, 2020.

COLUMBIA ACORN TRUST
By:	/S/    MATTHEW A. LITFIN
	Matthew A. Litfin, Co-President
By:	/S/    LOUIS J. MENDES
	Louis J. Mendes, Co-President

Pursuant to the requirements of the Securities Act of 1933, this amendment to the registration statement has been signed below by the following persons in the capacities and on the dates indicated.

Name	Title		Date
/S/    LAURA M. BORN*	Trustee and Chair	)
Laura M. Born		)
		)
/S/    MAUREEN M. CULHANE*	Trustee	)
Maureen M. Culhane		)
		)
/S/    MARGARET M. EISEN*	Trustee	)
Margaret M. Eisen		)
		)
/S/    JOHN C. HEATON*	Trustee	)
John C. Heaton		)
		)
/S/    CHARLES R. PHILLIPS*	Trustee	)
Charles R. Phillips		)
		)
/S/    DAVID J. RUDIS*	Trustee	)	May 15, 2020
David J. Rudis		)
		)
/S/    LOUIS J. MENDES	Co-President and Principal Executive	)
Louis J. Mendes	Officer	)
		)
/S/    JOHN M. KUNKA	Vice President and Treasurer (Principal Financial Officer)	) )
John M. Kunka		)

*	By:	/s/ Gwendolyn A. Williamson
	Name:	Gwendolyn A. Williamson** Attorney-in-fact

** Executed by Gwendolyn A. Williamson on behalf of each of the Trustees pursuant to a Power of Attorney incorporated by reference to the Registrant’s post-effective amendment No. 112 to the Registration Statement filed with the Securities and Exchange Commission on April 29, 2020.

Exhibit Index

Exhibit No.	Description
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase