A sliding mechanism (100) for use in a portable electronic device (500) is provided. The sliding mechanism includes a first plate (10), a second plate (20), a plurality of limiting structures (17), and a linkage module (30). The second plate is longitudinally slidably connected with the first plate. The limiting structures are secured on/to the first plate for limiting a position of the second plate with respect to the first plate. The linkage module is positioned between the first plate and the second plate and connects the first plate and the second plate. The linkage module particularly includes an elastic unit (34). The elastic unit is able to store spring energy that can be used to drive the linkage module. Specifically, such spring energy enables the second plate to automatically slide along the first plate after the second plate is manually moved an initial amount.