South Wales Fire and Rescue said its crews tackled the blaze throughout the night at the former White Hart Pub on Newbridge Road, Pontllanfraith.
They were called to the premises in the Sirhowy Valley village at about 19:30 GMT on Saturday.
Fire crews were back at the scene on Sunday checking for any hotspots after extinguishing the flames.
A joint investigation with police is now under way to establish how the fire was started, and who was responsible.
A fire at a disused pub in Caerphilly county was set deliberately, firefighters have said.