Arsonists broke into a house in Featherstone before starting a fire in the property on Saturday.
Fire crews from Featherstone and Pontefract Firefighters were called to a property on Lister Close at around 1.30pm.
Adam Smith, crew commander at Featherstone, said: “The fire was at an unoccupied property and it looked as though someone had broken in and set fire to a mattress in the bedroom.”
A police spokeswoman said paint had been thrown inside the property and a mattress or similar object was set alight.
She added: “Anyone who witnessed anyone acting suspiciously in the Lister Close area or who may have information about this offence is asked to call Normanton and Featherstone Neighbourhood Policing Team on 101.”
No-one was injured in the incident.