Samuel Gottlieb Gmelin (July 4, 1743? - June 27, 1774) was a German physician, botanist and explorer.

Gmelin was born at Tuebingen in a well known family of naturalists. His father was Johann Conrad Gmelin, an apothecary and surgeon. His uncle was Johann Georg Gmelin. Samuel earned his medical degree in 1763 from the University of Leiden at the young age of 18 (Silva et al., 1996). While living in Holland, Gmelin developed a keen interest in marine algae. In 1766 he was appointed professor of botany at St Petersburg. In the following year he was sent on an expedition to study the natural history of the Russian Empire. He explored the rivers Don and Volga, and the western and eastern coasts of the Caspian Sea. Whilst travelling in the Caucasus he was taken hostage by Usmey Khan of Khaïtakes and died because of ill treatment in captivity in Derbent. He was only 29 years of age.

Gmelin was the author of Historia Fucorum (1768), the first work dedicated to marine biology, dealing exclusively with algae and the first using the binomial system of nomenclature. It includes elaborate illustrations of seaweed and marine algae on folded leaves. However, algal specimens used by Gmelin in the Historia fucorum are thought to no longer exist (Dixon & Irvine, 1970). The results of his travels were published in Reise durch Russland zur èuntersuchung der drey natur-reiche (Trip through Russia to study the three natural provinces) (1770-1784, 4 vols.). The final volume was edited by Peter Simon Pallas.