Gerrit Smith Miller, Jr. (December 6, 1869 – February 24, 1956) was an American zoologist and botanist.
He was born in Peterboro, New York in 1869. He graduated from Harvard University in 1894 and worked under Clinton Hart Merriam at the United States Department of Agriculture. He became assistant curator of mammals at the United States National Museum in Washington in 1898 and was curator from 1909 to 1940, when he became an Associate in biology at the Smithsonian Institution. In 1906 he travelled to France, Spain and Tangier on a collecting trip.
In 1915, he published results of his studies of casts of specimens associated with the Piltdown Man, concluding that the jaw actually came from a fossil ape.