Heidelberg University said it had withdrawn Koch-Mehrin's academic title after an enquiry found that "substantial parts" of her 2000 doctoral thesis were copied from others.
"Given the variety and the systematic nature of the plagiarism, there can be no doubt that Ms. Koch-Mehrin appropriated others' intellectual property in her dissertation and used it as her own,” said Manfred Berg, a dean at the university and chair of the committee that has investigated the situation for the last two months.
Koch-Mehrin, 40, was once seen as a rising star of the pro-business FDP, Chancellor Angela Merkel's junior coalition partners, but her popularity had already waned before plagiarism allegations surfaced in May.
On May 11 she quit as head of her party in the European Parliament, as
deputy speaker of the parliament and as a member of the FDP leadership committee, but remained a member of the European body. She has been serving there since 2004.
On Wednesday Koch-Mehrin's spokesman said in a statement that the MEP was "surprised" and that her lawyers would examine the legality of the university's decision.
"I have known for 11 years that my doctoral thesis is no masterpiece... But (the university) awarded me the doctorate title in 2000 in full knowledge of all the glaring weaknesses," the statement said. "I deeply regret this decision."
Karl-Theodor zu Guttenberg, once the most popular figure in Merkel's cabinet, resigned as defence minister on March 1 after his doctorate was rescinded for massive plagiarism in his 2006 thesis.
His alma mater, Bayreuth University, found that "the standards of good scientific practice were obviously grossly abused and it was obvious that plagiarism was involved."
The episode earned the aristocratic minister the nickname "Baron Cut-and-Paste" and prompted the academic works of other figures to be scrutinised, including through collaborative websites.
Another casualty was Veronica Sass, the daughter of Edmund Stoiber, the long-serving former state premier of Bavaria who unsuccessfully ran for chancellor in 2002.