None of the 25 passengers aboard the bus was hurt.
It is believed the male elephant died instantly, while the bus driver, Narit Jitthrong, was transferred to a hospital.
The daily duty officer of Hang Chat Police Station, Captain Wiroj Saeng-eiam, who reported the accident on Chiang Mai-Lampang Rd, said the elephant had escaped from the Doi Phamueang Wildlife Sanctuary.
The animal belonged to the Elephant Reintroduction Foundation, and had been released into the wild.