A ball chain used in a linear guideway, at either end of the chain is formed a protruded connecting block, the connecting blocks each has an abutting surface that is parallel to a radial direction of a center of the radius of curvature of the ball chain, the abutting surfaces of the connecting blocks of the spacers at both ends of the chain are mated with each other for limiting axial rotation of the ball chain. Due to the two connecting blocks at the end of the ball chain that has entered the return path protrude out of the groove, the end of the chain within the return path will use the abutting surface to limit the end of the chain that has not entered the return path and to guide the end of the chain, which has not entered the return path, into the return path smoothly, thus improving the operating smoothness of the chain.