The former El Rancho restaurant, at the corner of Legion Road and West Mountain Drive, was engulfed in flames when firefighters arrived at 5 a.m., authorities said.
Police closed Legion Park Drive to Sandy Valley Street and West Mountain Drive from Sycamore Street to Camden Road.
Investigators called the fire suspicious, noting the restaurant has been vacant since 2013 and has no electricity. Also, they said, vandals have targeted the building in the past.
The fire appears to have started from the center of the building, authorities said, but investigators haven't yet determined the cause.
There were no reported injuries.