The accident happened at Ramche village in Rasuwa district, 150 kms north of Kathmandu near Nepal's border with Tibet.
Those killed include 18 men and 12 women, police said.
About 30 passengers, who were injured in the accident have been admitted to Dhunche Hospital for treatment.
The accident occurred as the driver lost control and the bus rolled down the hill.
Nepal Army personnel, police and local people were involved in rescue operation after the crash.