Firefighters from Dearne station were called to a shop front alight on Adwick Road in Mexborough at 11.45pm and were on scene for 30 minutes.
Earlier that evening, a crew also from Dearne were called to a Ford Fiesta alight on Barnsley Road in Wombwell. They received the call at 9.40pm and stayed on scene until 10.25pm.
Both fires were believed to had been started deliberately, said a spokeswoman from South Yorkshire Fire and Rescue.
Arsonists set light to a vehicle in Edlington at 2.30am on Saturday.
A crew from Edlington were called to a Siver VW Golf on fire on Blackwood Avenue. They left the scene almost an hour later.