A parking brake assembly for a railway car includes a ratchet mounted for rotation on a threaded piston rod of a brake actuator and a holding pawl engageable with the ratchet for maintaining a push rod of the parking brake assembly to apply braking force when the air pressure is lost in the brake pipe and releasing the push rod to accordingly release the braking force when the supply of air pressure in the brake pipe is restored. An operating lever and a cylinder connected thereto are provided for selectively rotating the holding pawl. Valve is provided for supplying air pressure to and evacuating it from the cylinder. Release mechanism is provided for manually releasing the braking force. The parking brake assembly is employed with either truck-mounted or carbody-mounted braking system.