The present invention is to provide a retractable lens assembly for automatically projecting or retracting its lens in response to a display of an electronic device (e.g., cellular phone or notebook) incorporating a lens assembly being opened or closed, which includes a downwardly extended first projection at one end of a rotatable unit being fixed in a body of the electronic device, a second projection extended from an outer surface of a shaft at the other end of the rotatable unit being fixed in the display, and a lens module being rotated in one direction in response to the display being opened in a manner similar to extending the cosmetic paste of a lipstick for projecting a lens from the lens assembly for taking pictures or photographs.