The female elephant's skin, tail, tusks, ears and many internal organs had been removed, the Tuoi Tre newspaper said, quoting local forest rangers.
It was not immediately clear why it was mutilated, but elephant ivory and other body parts are prized in Vietnam for decoration, as a talisman, and for use in traditional medicine.
Local residents reportedly recently saw an elephant wandering in the forest about 40km from the Laos border.
They are more commonly found in Vietnam's Central Highlands.
Vietnam is home to some 100 wild elephants, according to state media, but habitat loss, human-animal conflict and poaching are seen as responsible for a sharp decline in the population in recent decades.
Environmental group World Wildlife Fund (WWF) says Vietnam is one of the world's worst countries for trade in endangered species.
Vietnam outlawed the ivory trade in 1992 but shops can still sell ivory dating from before the ban.