Elephants lack natural predators in nature, largely as a result of their size. They are too big for most would-be predators to take down safely and eat. Humans are the primary predator of elephants, as people still hunt elephants for their ivory, meat and bones.
Some predator animals have been known to target young elephants when they become separated from their parents. Crocodiles, lions, and sometimes even leopards and hyenas target young elephants as prey. According to Wikipedia, lions have been observed attacking infant and juvenile elephants in Chobe National Park in Botswana, though they will not approach an adult elephant.