Six fire engines and an aerial ladder platform have raced to the Hob Inn off Station Road after reports of flames and smoke coming from the roof.
Traffic is being diverted from the scene of the blaze which is believed to have started around 4pm.
A spokesperson for Lancashire Fire and Rescue Service said: "We have an incident at a pub in Church Road, just off Station Road, Bamber Bridge.
"The building is a pub with a large thatched roof.
We have six fire engines there and also an aerial ladder platform. It is quite a large pub with quite a large roof.
"As far as we know there are no casualties."