Abstract: A structurally improved rail-type device for mechanically splicing optical fibers while reducing the splicing loss is disclosed. The above splicing device not only has a cladding clamp with a seesaw structure thereby easily splicing the optical fibers, it also separately moves the covers relative to the body to easily perform the tuning operation. Due to coating clamp's protrusions and body's slots engaging with each other, the coating clamp exclusively vertically move relative to the body and prevent the optical fibers from being axially thrust. The splicing device further seperately clamps the coating and cladding parts of the optical fibers, thereby preventing the spliced fibers from breaking due to tensile or torsional force. The sliding motion of the covers relative to the body is achieved by the rails of the covers and rail grooves of the body.