It is the second horse death to be reported at the park in the span of four days after six weeks without a horse dying at the track.
The horse, a 3-year-old gelding named Spectacular Music, sustained a fatal injury to his pelvis Sunday while racing, park officials said in a statement.
"Equine pelvic injuries are rare, and further evaluation is being conducted by the California Horse Racing Board, per protocol, to understand what could have caused this uncommon injury," park officials said.
On Friday, a 3-year-old gelding named Commander Coil died during training when it suffered a shoulder injury and was euthanized.
Sen. Dianne Feinstein, who recently called for a suspension of racing at the track during an investigation of the cause of the horse deaths said in part in a statement, "Two more horses have died at Santa Anita Park over the last four days, a stark reminder that the problems that led to 23 dead horses over three months haven't disappeared. How many horses must die before serious action is taken?"