The chapel on Healdfield Road in Castleford went up in flames at around 9pm on March 30.
Police said: "We would like to hear from anyone who has seen anything suspicious in the area prior to the fire or anyone fleeing the scene. Reports have already been taken and enquiries are ongoing."
Anyone with details can call 101 quoting crime number 13220171256.
Fire crews from several stations were called to the chapel, where they found 80 per cent of the building consumed by flames.