Firefighters responded to the one-alarm fire at 330 Western Ave. at about 8:15 p.m., fire officials said.
Upon arrival, firefighters found heavy smoke coming from a small building that was originally a gas station, and most recently a Mexican restaurant, officials said.
Flames were mainly burning the back of the building, which has been empty for more than a year, the fire department said.
The Petaluma Fire Department was able to control the fire within minutes using one hose line and by cutting a ventilation hole in the roof.
The cause of the fire is unknown, but investigators are considering the fire suspicious since there was no electrical power to the building, according to the fire department.
Two witnesses also reported seeing a vehicle leaving the area at the time of the fire.
No was injured in the fire, but officials notified a building representative to board up and secure the building.
The Petaluma Fire Department sent two engines, one truck, two paramedic units, a battalion chief, and the fire marshal to control the fire.
The Rancho Adobe Fire Protection District and Cal Fire also sent engines to assist with the fire.
All fire units left the scene at about 10:20 p.m., officials said.