The fire broke out at the White Swan pub in Balby Road, Balby at around 4.30am on Saturday morning.
Two engines from Doncaster station and one from Edlington station were called out to the blaze.
Fire crews left the scene at around 5.40am, after the fire had been extinguished.
A South Yorkshire Fire and Rescue spokesman confirmed the fire is believed to have been started deliberately.
South Yorkshire Police have been contacted for comment on this story.