Justus Olshausen (9 May 1800, Hohenfelde – 28 December 1882) was a German orientalist who made contributions to Semitic and Iranian philology.
Olshausen was born in Hohenfelde, and studied at Kiel, Berlin and Paris, where he was a student of Silvestre de Sacy (1758–1838).
In 1852 he was removed from his position at Kiel by the Danish government, which he had energetically opposed, and subsequently became a professor of Oriental languages at the University of Königsberg.
In 1860, he became a full member of the Prussian Academy of Sciences, and in 1874 was appointed counselor to the Ministry of Education in Berlin.
Olshausen specialized in Semitic and Persian philology, and was a pioneer in Pahlavi studies.