William Henry Howell (February 20, 1860 - February 6, 1945) was an American physiologist. He pioneered the use of heparin as a blood anti-coagulant. He graduated from Johns Hopkins University in 1881. He taught at the University of Michigan and at Harvard before becoming professor at Johns Hopkins in 1893. He was dean of the medical school from 1899 to 1911. He was associate editor of the American Journal of Physiology. He died in 1945 at the age of 84.