The Frye Agency, an insurance and real estate agency in Braintree, caught fire early Tuesday morning, closing off a section of Washington Street.
Nearby fire departments, including Weymouth, Holbrook and Quincy, helped put out the three-alarm fire just after 2 a.m. at 1579 Washington Street.
Massachusetts State Police, Braintree fire officials and arson units are investigating the commercial building fire.
No injuries were reported. No further information was immediately available.