A sliding mechanism used in a portable electronic device is described. The sliding mechanism includes a body section, a cover section, a rolling disk and a coil spring. The rolling disk is fixed to the cover section. A center of the coil spring is fixed to a center of the rolling disk. An end of the coil spring is fixed to a periphery of the rolling disk. When the rolling disk rotates relative to the body section, the coil spring generates a force towards or against the sliding direction of the cover section.