Annette Schavan is the second minister in Chancellor Angela Merkel's Cabinet to lose a doctorate because of plagiarism. Former Defence Minister Karl-Theodor zu Guttenberg resigned in 2011 after it emerged he copied large parts of his thesis.
Opposition politicians say Schavan is now in an untenable position as education minister and must step down.
Duesseldorf's Heinrich Heine University voted Tuesday to remove Schavan's doctorate after a thorough review of her 1980 thesis undertaken after an anonymous blogger raised plagiarism allegations.
Speaking on a trip to South Africa on Wednesday, Schavan said she "will not accept" the school's decision and would take legal action against it.