The ammunition were recovered from Nagaland Express this morning when the train halted at Hojai station, police sources said.
A total of 566 rounds of bullets were found inside five bags which were lying unclaimed in one of the compartments.
The bullets were of AK-47 assault rifles, 9 mm pistols and Insas rifles, police said.
No arrest have been made so far but police have launched an investigation in this regard.
It is suspected that the ammunitions were being transported from Dimapur in Nagaland.