Gérard Daniel Westendorp (8 March 1813, The Hague – 31 January 1869, Dendermonde) was a Dutch born, Belgian military physician and botanist. He studied medicine at the Ecole de Médecine de Bruxelles, later working as a student-physician in Antwerp. Around 1834, he became a naturalized citizen of Belgium, subsequently serving as an assistant army and navy physician, later spending his career as a "regular doctor" in the Belgian army. Westendorp's botanical specimens are preserved in the Jardin Botanique National de Belgique.