Leonard James Spencer CBE FRS (7 July 1870 – 14 April 1959) was a British geologist. He was an Honorary member of the Royal Geological Society of Cornwall, and also a recipient of its Bolitho Medal. He was president of the Mineralogical Society of Great Britain and Ireland from 1936 to 1939. In mineralogy Spencer was an original investigator who described several new minerals, including miersite, tarbuttite, and parahopeite. He also did important work as a curator, editor and bibliographer.
His daughter, Penelope Spencer became a successful free-style dancer and choreographer.