Haldor Frederik Axel Topsøe (29 April 1842 in Skælskør, Slagelse Municipality, Denmark – 31 December 1935 in Frederiksberg, Denmark) was a Danish chemist and crystallographer.
Topsøe took Magisterkonferens in chemistry in 1866 and doctorate for a chemical-crystallographical work of selenium-sour salts.
He worked as assistant at the Natural History Museum 1863–1867 and at the chemistry laboratory of University of Copenhagen 1867–1873.
In 1872, he received a gold medal of Royal Danish Academy of Sciences and Letters, of which he was member from 1877, for a great crystallographical-optical work together with the physicist Christian Christiansen (1843–1917).
In 1884 he participated in the oceanographic expedition to west Greenland on the gunboat HDMS Fylla.