The remains were found at the weekend in the bush at a private game park near Hoedspruit in the northern province of Limpopo, where animals have been poached in increasing numbers over recent years.
"It seems the victim was poaching in the game park when he was attacked and killed by lions. They ate his body, nearly all of it, and just left his head and some remains," Limpopo police spokesman Moatshe Ngoepe told AFP.
Last year, several lions were found poisoned near a farm in the same province with their heads and paws sawn off.
Lion body parts are used in traditional medicine.
Poachers also often target rhinoceroses in South Africa's game parks to feed a booming demand for rhino horn in China, Vietnam and other Asian countries, where it is believed to have medicinal qualities.