A linear motion guide unit is disclosed, in which a slider fitting over a guide rail for movement is comprised of three components save rolling elements. The three components are joined together in the slider with using no fastener such as threaded fasteners, but just with fit-engagement that makes it possible to shrink the slider down in size. The three components are made up of a carriage made therein with raceway grooves and return passages, an upper component applied to the carriage to fit into recesses on the top surface of the carriage, and a lower component applied to the carriage to fit into recesses on the bottom surface of the carriage. The upper and lower components are joined together with the help of fit-engagement of hooks and hook holes, with holding firmly the carriage between them.