The University of Dusseldorf declared Annette Schavan's doctoral thesis "invalid" and revoked her Ph.D., Der Spiegel reported Wednesday.
Schavan has been under a cloud for some time over allegations she plagiarized parts of her thesis.
Announcing the revocation Tuesday night, Bruno Bleckmann, a professor of ancient history at the university, said a committee had voted 12-2 to annul the doctorate.
Bleckmann said the committee found while a doctoral student, Schavan had "systematically and deliberately presented intellectual efforts throughout her entire dissertation that were not her own,"
He said large portions of her thesis had been taken from other sources without adequate attribution
Immediately after Bleckmann's statement, Schavan's lawyer said he would challenge the revocation in court.
"There was no cheating involved," he said in a statement.
The university's decision may force Schavan to step down from Chancellor Angela Merkel's cabinet. The Greens, the Left Party and the Pirate Party are already demanding her resignation.
Defense Minister Karl-Theodor zu Guttenberg resigned in 2011 after he was found to have plagiarized large portions of his doctoral thesis.