The shocking incident occurred just outside the family’s home in Calabasas, in the US state of California. The mountain lion was later tracked down and killed by a wildlife officer.
The child was playing near their home on Thursday. The beast dragged him “about 45 yards”, California Department of Fish and Wildlife said.
The mother rushed to the little boy’s aid and started “punching and striking the mountain lion with her bare hands”, according to spokesman Patrick Foy.
The boy suffered significant injuries to his head and upper torso but is in a stable condition at a Los Angeles hospital, according to Mr Foy.
“The true hero of this story is his mom because she absolutely saved her son’s life,” he said.
“Due to its behaviour and proximity to the attack, the warden believed it was likely the attacking lion and to protect public safety shot and killed it on sight,” the wildlife department said in a statement.
The lion was crouching in bushes at the house with its “ears back and hissing” at the wildlife officer, Mr Foy said.
DNA tests were conducted to confirm the animal shot was the beast that attacked the child.
One of the mountain lions in the area was tranquilised. But after being tested it was released back into the wild as it was not involved.
“There is much angst with people who are furious that we killed the mountain lion responsible for attacking that boy,” Foy told the Los Angeles Times.
“It was trying to kill and eat that child, unfortunately.
“Many members of the public don’t want to ever think of a human being as a prey item. It does happen sometimes.”
According to California Department of Fish and Wildlife, this is the first mountain lion attack on a human in 25 years in Los Angeles.