The five year old suffered injuries to his face, head and neck, and his mother sustained minor injuries to her hand and legs in the attack yesterday in a rural area 10 miles (16 kilometers) northwest of Aspen, the Pitkin County Sheriff's Office said.
The boy was outside in the yard playing with his older brother when the mother heard screams.
"The mother ran outside, saw the mountain lion on her son and was able to physically remove her son from the mountain lion," the sheriff's office said in a statement.
Deputies and a law enforcement officer from the US Forest Service went to the house and found the mountain lion still in the yard.
The animal was put down by the Forest Service officer.