A posting on a Web site devoted to Gies said she died following a short illness but there were no other details, The New York Times reported.
Gies was the last surviving member of the small group who protected Frank. She preserved the journal the young Frank kept during her seclusion in Amsterdam, Netherlands -- a journal that was published as "The Diary of Anne Frank."
Gies and her husband, along with three other people, provided a hiding place for Anne Frank and her parents and sister, as well as four other Dutch Jews, who managed to elude capture by Nazis for 25 months before an anonymous tipster turned them in.
In a memoir published in 1987, Geis rejected the notion what she and the others did was heroic.
"I stand at the end of the long, long line of good Dutch people who did what I did and more -- much more -- during those dark and terrible times years ago, but always like yesterday in the heart of those of us who bear witness," she wrote in "Anne Frank Remembered."
Gies spoke extensively during the 1980s about intolerance, and the West German government in 1989 presented her with its highest civilian medal, the Times said. Queen Beatriz of the Netherlands knighted Gies in 1996.