The present invention relates to a lift assist device which is used to alleviate the physical demands for the operation of a heavy percussion power tool, such as a pneumatic jackhammer, by facilitating lifting and freeing the percussion power tool. In general, the lift assist device contains an actuating cylinder with a lifting foot attached to the outside end of its piston rod and a control unit which comprises a directional control valve and a hand lever. The control unit is on the top of the lift assist device and can be used to control the lifting speed and height. The lift assist device is secured to the body of the percussion power tool with one or more mounting elements.