The bus, traveling on a rural highway, was ripped apart when it drove over the mine near Badarmude village, killing 25 people instantly, an army official said on customary condition of anonymity. Army officials are not allowed to reveal their names in Nepal for security reasons.
Another 36 people were wounded, some of them critically, and were taken to nearby hospitals, the official said.
Badarmude, in Nepal's Chitwan district, is about 180 kilometers (112 miles) southwest of the Nepalese capital Katmandu.
Police suspect the land mine was planted by Maoist rebels, who have been fighting since 1996 to abolish Nepal's constitutional monarchy and set up a communist state. The guerrillas claim to be inspired by Chinese revolutionary Mao Zedong.
'The king is weakening gradually'
The guerrillas have stepped up violence since February 1, when King Gyanendra took control of the government and imposed a state of emergency that was lifted in April.
The rebels responded to the king's power grab by shutting down highways and calling a general strike. They have repeatedly refused government calls for peace talks.
The king said the move was necessary to quell the communist insurgency, which has left more than 11,500 people dead since 1996.
