A spokesman for South Yorkshire Fire and Rescue said the force was alerted to the blaze at the former Mexborough fire station in Highwoods Road shortly after 2am on Saturday, and crews were on the scene within minutes. The spokesman added: "The fire was contained to the first floor, former accommodation area of the old fire station, which was well alight.
"Around 25 firefighters from Dearne, Rotherham and Edlington fire stations used jets, hose reels and an aerial ladder platform to bring the fire under control. The last crew left the scene at 6.33am.
"The cause of the fire is believed to be deliberate."
Mexborough fire station closed in April this year to be replaced by a 4m state-of-the-art station at nearby Manvers, which is home to four watches of 14 firefighters.
It has community and training rooms, a gym, 12 beds and a "multi-faith and study" room.