Police said the boy, 16, was arrested after the fire at The Orchard in Quedgeley. A woman escaped from the building but a dog died in the blaze.
Firefighters from Gloucester, Stroud, Painswick and Cheltenham were called to the blaze in the early hours.
The boy was released on police bail on Friday evening, pending further inquiries.
Richard Smith from Gloucestershire Fire and Rescue said the fire was "very severe".
He said the building was currently too unsafe to enter.
Mr Smith said a "full fire investigation" was under way at the pub in Olympus Park and the service was working with Gloucester Police.
He added about 50 firefighters were called to the blaze and stopped it from spreading to neighbouring buildings.
A teenager has been arrested on suspicion of arson after a pub in Gloucester was destroyed by fire.