Gustaaf Adolf Frederik Molengraaff (27 February 1860 – 26 March 1942) was a Dutch geologist, biologist and explorer. He became an authority on the geology of South Africa and the Dutch East Indies. Gustaaf Molengraaff studied mathematics and physics at Leiden University. From 1882 he studied at Utrecht University. As a student he made his first journey overseas when he joined the 1884–1885 expedition to the Dutch Antilles led by Willem Frederik Reinier Suringar and Karl Martin. He became PhD with a thesis on the geology of Sint Eustatius. He studied crystallography in Munich, where he also took the opportunity to study the geology of the Alps nearby.