A linear actuator includes a slide, a first half return member, a second half return member and a slide block. The first and second half return members are hollow frames and sleeved onto the rail. A circulation path can be formed when the first and second half return members and the slide block are assembled together, the second half return member is directly disposed in the first radial gap of the first half return member, and the slide block is directly disposed in the second radial gap of the second half return member. Furthermore, there is no level difference in the first and second return grooves of the two half return members, which will prevent noise caused during movement of the rolling elements, reduce impact of the rolling elements against the circulation path, and therefore extending the life of the linear actuator.