An adjustable drum pedal assembly has a rotated shaft, a drive device and a chain. The rotated shaft has a fixed bracket formed on the rotated shaft and has a screwed hole. The drive device is mounted on the rotated shaft and has a base, a mounting panel and a bolt. The base is combined with the fixed bracket and has an adjusting groove, a mounting recess, a securing hole and an elongated through hole. The mounting panel is mounted to the rear end of the base. The bolt is screwed into the screwed hole. The chain is mounted between the drive device and the drum pedal and has a fastener screwed into the securing hole in the base to connect the chain to the drive device.