Gustave Charles Sap (21 January 1886 – 19 March 1940) was a Belgian politician and minister for the Catholic Party. Sap was also professor at the Catholic University of Leuven (Leuven, Belgium). During his professional career, he was active in the Flemish movement, agriculture and business. In 1920, he married Antoinette Gylsen, daughter of the Antwerp shipowner Henry Gylsen, and together they had five daughters and one son. Gustave Sap was the father-in-law of André Vlerick, and .