QuickLinks -- Click here to rapidly navigate through this document

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 6-K

Report of Foreign Private Issuer

Pursuant to Rule 13a-16 or 15d-16
of the Securities Exchange Act of 1934

For the month of April, 2004

Commission File Number: 001-10378

AVENTIS
(Translation of registrant's name into English)

67917 Strasbourg CEDEX 9
France
(Address of principal executive offices)

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): 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)(7): o

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): Not applicable

Signatures

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.

		AVENTIS (Registrant)
Date: April 22, 2004		By:	/s/ DIRK OLDENBURG Name: Dirk Oldenburg Title: General Legal Counsel

EXHIBIT LIST

Exhibit		Description
99.1		Press Release, dated April 21, 2004, announcing Aventis' clarification to the AMF regarding its proposed draft resolution to issue warrants.

QuickLinks

Signatures
EXHIBIT LIST

AVENTIS 6-K