The fire department was called to the EuroMarché store at about 3:30 a.m. on Wednesday.
Police Const. Simon Delorme said the front window of the business was broken when firefighters arrived on the scene, near the corner of Fleury Street and Saint-Michel Boulevard.
He said the building's sprinkler system had mostly extinguished the fire inside.
Last Wednesday, another EuroMarché store in Ahuntsic was the target of a firebombing attack.
Delorme said the fire department has handed over the investigation to the Montreal arson unit.