PARIS—A French appeals court ruled on Wednesday to uphold preliminary charges of aggravated pimping against former International Monetary Fund chief Dominique Strauss-Kahn.

Mr. Strauss-Kahn had turned to the appeals court saying the charges are groundless and should be dropped. Mr. Strauss-Kahn's lawyers have said their client participated in sex parties, notably in Washington, but didn't know that some of the women present may have been prostitutes.

The team of three lawyers defending Mr. Strauss-Kahn said their client would appeal Wednesday's ruling with a higher court.

French investigating magistrates filed the pimping charges against Mr. Strauss-Kahn in March as part a broader judicial investigation into an alleged prostitution ring based out of the northern French city of Lille.

Prostitution is legal in France; pimping isn't. To indict Mr. Strauss-Kahn, the Lille magistrates would have to prove that he played an organizational role in the alleged prostitution ring.