A collapsible toy air gun with at least two tapered tubular sections adapted to be cooperatively joined coaxially, at least one supporting plate, a diaphragm and a resilient string. The tapered tubular sections are correspondingly sized concentrically to form a tubular body having a larger and an opposite smaller opening end in the extended operational position. At least one supporting plate is mounted on the circumferential surface of the tubular body to maintain the tubular sections in the extended position. The diaphragm is mounted transversely across the larger opening end of the tubular body with a pull knob and back support secured to the diaphragm. The resilient string is mounted across the smaller opening end of the tubular body through the back support.