Johannes Jacobus "Jan" Gregoor (April 9, 1914 – May 20, 1982) was a Dutch painter and art educator.
Gregoor was born in The Hague, where he studied at the Dutch Royal Academy of Art.
During World War II, he put his art skills in service of the Dutch resistance, when (sometimes along with Max Velthuijs) he forged stamps in identity papers of people in hiding.
Among his many students were Helen Berman, Frans Clement, Els Coppens-van de Rijt, Jan Dibbets, and Hans van Vroonhoven.
His brother, Nol Gregoor, was a famous Dutch art critic and essayist.