The present invention provides a disposable syringe and a push rod for use in a disposable syringe. The push rod comprises a proximal end, a distal end and an axis extending through the proximal end and the distal end. The distal end of the push rod is provided with a snap-fitting mechanism and a stop flange located at a proximal side of the snap-fitting mechanism. The stop flange comprises a main body portion formed about an axis of the push rod and a plurality of finger-like portions extending from the main body portion in a direction away from the axis of the push rod. According to the present invention, a smaller push force continues to be applied to the push rod upon completion of the injection, thereby achieving an additional stroke needed when the distal end of the push rod snap-fits with the needle seat and meanwhile lessening the patient's pains.