Leopold Gmelin (2 August 1788 – 13 April 1853) was a German chemist.
Gmelin was the son of Johann Friedrich Gmelin. He studied medicine and chemistry at Göttingen, Tübingen and Vienna, and in 1813 began to lecture on chemistry at Heidelberg, where in 1814 he was appointed extraordinary-, and in 1817 ordinary-, professor of chemistry and medicine. He was the discoverer of potassium ferricyanide (1822), and wrote the Handbuch der Chemie (first edition 1817–1819, 4th ed. 1843–1855), an important work in its day, which was translated into English for the Cavendish Society by Henry Watts in 1848–1850. Friedrich Wöhler finished his study of medicine at Gmelin's laboratory. Gmelin resigned his chair at Heidelberg in 1852, leaving Robert Bunsen to succeed him, and died in Heidelberg.
Gmelin and his wife in 1820
German postal stamp featuring Gmelin