A linear motion system comprises a guiding member, a moving member, a plurality of rolling members and a preload adjusting module. The moving member is slidably disposed on the guiding member. The moving member and the guiding member together form a circulation path. When the guiding member moves with relative to the moving member, the moving member can generate a linear movement with relative to the guiding member. The rolling members are accommodated in the circulation path. The preload adjusting module is disposed on the moving member, and comprises a preload assembly and a preload regulator. The preload regulator applies a thrust to the preload assembly to adjust a preload value generated by the rolling members and applied to the moving member.