Georg Ossian Sars (April 20, 1837 – April 9, 1927) was a Norwegian marine biologist.
Georg Ossian Sars was born on April 20, 1837, in Kinn, Norway (now part of Flora), the son of Michael Sars and Maren Sars; the historian Ernst Sars was his elder brother, and the singer Eva Nansen was his younger sister. He grew up in Manger, Hordaland, where his father was the local priest. He studied from 1852 to 1854 at Bergen Cathedral School, from 1854 at Christiania Cathedral School, and joined the university at Christiana (now the University of Oslo) in 1857. He indulged his interest in natural history while studying medicine; having collected water fleas in local lakes with Wilhelm Lilljeborg's works, he discovered new species, and this resulted in his first scientific publication. Georg Ossian Sars had a good memory and excellent drawing skills, and illustrated some of his father's zoological works.
Sars was a founding investigator of ichthyoplankton. In 1864, he was commissioned by the Norwegian government to investigate fisheries around the Norwegian coast. One of his first discoveries was that the eggs of cod are pelagic, that is, they inhabit the open water column. He continued to receive the patronage of the government throughout his career. Sars' primary research focus was on crustaceans and their systematics. He described many new species in his career, including in his magnum opus, An Account of the Crustacea of Norway. He was awarded the Linnean Medal in 1910.
Georg Ossian Sars never married, and died on April 9, 1927 in Oslo. He is remembered in the scientific names of a number of marine invertebrates, as well as the journal Sarsia, and the flagship of the Norwegian research fleet, the RV G.O.Sars.