Abstract: A device for preventing derailment of a bicycle chain of a bicycle. Upper and lower guide members are positioned strategic to a drive sprocket of the bicycle to guide and maintain the chain in engagement with the drive sprocket regardless of the tension of the chain. The upper and lower guides force the chain to be engaged a longer circumferential distance on the drive sprocket to prevent the chain from jumping off the drive sprocket. Circular guards are mounted on each side of the drive sprocket to protect the drive sprocket and the chain entrained thereon from impact. The spacing of the circular guards provides a channel for receiving the chain as it traverses the drive sprocket.