The ammunition, buried underground, was recovered during construction work from a part of Usha Bagan Primary School in Merapani area bordering Nagaland.
Altogether 186 rounds of ammunition, 170, .303 rifles and 16, 9 mm pistols were recovered, the sources said.
The police suspect that the ammunition could have been been hidden by local people or militants several years ago during skirmishes between Assam and Nagaland.