The bus travelling from Moronoi in the district to Guwahati collided with the truck coming from the opposite district at Amjunga under Dudhnoi police station on NH-37, police said.
Two passengers and conductor of the bus died on the spot, while 17 passengers were injured, three of them seriously.
The accident victims were identified as bus conductor Binodhar Medhi and passengers Pujeswari Rabha and Suleman Khaklary, they said.
The injured were admitted to Goalpara Civil Hospital while the three seriously wounded referred to the Gauhati Medical College Hospital.