QuickLinks -- Click here to rapidly navigate through this document



UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

Form 6-K

REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13a-16 OR
15d-16 UNDER THE
SECURITIES EXCHANGE ACT OF 1934

For the month of May 2006

Commission File Number: 001-16829

Bayer Aktiengesellschaft
Bayer Corporation*


(Translation of registrant's name into English)

Bayerwerk, Gebaeude W11
Kaiser-Wilhelm-Allee
51368 Leverkusen
Germany


(Address of principal executive office)

        Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.    Form 20-F  ý    Form 40-F  o

        Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):             

        Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):             

        Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934. Yes  o    No  ý

        If "Yes" is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): 82-                         .

*
Bayer Corporation is also the name of a wholly-owned subsidiary of the registrant in the United States.




Exhibit List
  Description

99.1

 

English translation of notice published in the
Börsen-Zeitung on May 26, 2006


SIGNATURE

        Pursuant to the requirements 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.

    BAYER AKTIENGESELLSCHAFT (REGISTRANT)

 

 

By:

/s/  
DR. ROLAND HARTWIG      
Name:  Dr. Roland Hartwig
Title:    General Counsel

 

 

By:

/s/  
DR. ALEXANDER ROSAR      
Name:  Dr. Alexander Rosar
Title:    Head of Investor Relations

Date: May 26, 2006




QuickLinks

SIGNATURE