She's the first filly to win the Belmont since Tanya in 1905.
Rags to Riches held off Preakness winner Curlin with Tiago finishing third.
The victory by Rags to Riches ends a long Triple Crown losing streak for trainer Todd Pletcher. He had been winless in 28 previous Triple Crown races, including six Belmonts. It also was the first Triple Crown win for jockey John Velazquez, who had been oh-for-20 in previous Triple Crown events.
Rags to Riches paid ten dollars and 60 cents for a two-dollar bet.