Parking Brake Mechanism, particularly suited for an All-Terrain Vehicle (ATV) with a security feature is manually engaged by foot or hand and is automatically disengaged by spring action when the ATV operator presses the vehicle brake pedal to shift the transmission lever into “drive”. The present invention also allows the operator to secure the vehicle with the parking brake engaged. The vehicle brake mechanism is activated and held on by the parking brake unit; therefore, immobilizing the vehicle.