Toronto Police were called just after 1 p.m. Monday to the discount store after someone dropped it off as a donation in an army surplus bag.
The Emergency Task Force and bomb disposal unit were also called in, Const. Tony Vella said.
The store was evacuated, and the grenade was taken away for examination.
Vella said the grenade - made of metal and very much the "real" thing - was not a threat.
It was dropped off at the store ... in the bag, but it wasn't active," Vella said, adding a knife was also found in the bag.
Police are investigating the strange and ominous drop-off, but Vella could not say if it would be possible to trace who dropped the bag off.