Abstract: A protective jacket is formed of two symmetrical half-round shells molded from rigid, transparent plastics and fastened together by hooks thereof and secured to the electric wire of a light string to protect a bulb. Each half-round shell has two opposite pairs of half-round holes for the passing of the electric wire, two partition ribs defining a chamber for holding the bulb, an upright stop plate stopped at one end of the bulb to separate the lead wires, and a longitudinal series of upright stop rods for stopping the bulb against the upright stop plate.