August Belmont, Jr. (December 28, 1851-December 10, 1924), was a son of August Belmont, Sr.

The younger August Belmont was an 1875 graduate of Harvard University, where, as a sprinter, he supposedly introduced spiked track shoes to the United States. Upon his father's death, he inherited a position as head of the Belmont banking house. He was an important early investor in the New York Subway, and is responsible for the creation of Belmont Park. He served as Director of the National Park Bank.

August Belmont, Jr. was an avid thoroughbred racing fan and the prestigious Belmont Stakes was named for him. For a number of years, Belmont owned one of the best racing stables in America and five times horses from his own stable won the Belmont Stakes. He also had horses competing in England and in 1908 his colt "Norman" won the Two Thousand Guineas.

Following the United States' entry into World War I, Belmont, at age 65, volunteered to assist and was sent to France by the U.S. Army. At home, his wife named a new foal "My Man O' War" in honor of her husband but because of his age and the uncertainty as to the War's end, August Belmont, Jr. decided to disband the stable and with the "My" dropped from the name, Man O' War was sold to Glenn Riddle Farm in Maryland.

His widow Eleanor Robson Belmont died at 100 in 1979.