The fire in Cleveland Street in the town centre was discovered at 9pm yesterday.
Firefighters said they found flames in the kitchen.
The flat was unoccupied at the time.
Anyone with information should call South Yorkshire Police on 101.
Flat set alight in arson attack in Doncaster
A flat was set alight in an arson attack in Doncaster.
By The Newsroom
Friday, 3rd November 2017, 8:10 am
Updated Tuesday, 12th December 2017, 12:02 pm