The elephant 'Babul' suddenly threw his mahout Nirmal Barman off its back last night and trampled him to death in the Burapahar range of the park, said Divisional Forest Officer (DFO) D D Gogoi.
The elephant along with other jumbos carrying forest guards were on patrolling duty when the incident took place.
They were returning to their camp at Borholla inside KNP after recovering the carcass of a rhino that was killed by poachers and its horn removed, Gogoi said.
The cause for the sudden attack was being investigated and the pachyderm kept safely away from other animals.
Meanwhile, two rhinos were killed by poachers and their horns taken away yesterday in Bagori range and Burapahar range of the park.
In the first month of this year five rhinos from the park have been killed by poachers and their horns taken away.