The incident occurred on late Monday night but it was reported to the police yesterday.
Suspected militants hurled two grenades at the TA at Koirengei on the outskirts of Imphal at around 9 PM on Monday, the police said.
While one grenade exploded seriously injuring Lance Naik Jagga Singh, the other did not explode, the police said.
Singh died on way to Army hospital at Leimakhong, 25 km from here.
Singh of 165th TA was attached to 107 Engineer Regiment under Red Shield division of the Army for some construction work.
No individual or group has claimed responsibility for the attack.