A catcher's leg guard includes an ankle pad, a shin pad, a knee pad, a thigh pad, a plurality of connecting belts connected between the knee pad and the thigh pad, a plurality of adjustment straps respectively stitched to the shin pad, the knee pad, and the thigh pad, and a plurality of breathing gauze cloth linings respectively covered on the ankle pad, the shin pad, the knee pad and the thigh pad at an inner side for direct contact with the user's skin, air vents extended through the ankle pad, the shin pad, the knee pad and the thigh pad in air-communication with open spaces in the breathing gauze cloth linings, and an inner knee pad detachably adjustably fastened to the knee pad with hook and loop materials, the ankle pad, the shin pad, the knee pad and the breathing gauze cloth linings being respectively coated with a micro-organism resisting and mildew-retarding treatment agent.