Various embodiments may relate to an end cap for a lamp tube of an illuminating device, including a mounting ring fixedly mounted to one end of the lamp tube by means of an assembled end, and a cover plate for closing the mounting ring at a free end. The end cap further includes a rotating ring mounted between the mounting ring and the cover plate at the free end, the cover plate rotatably closes the mounting ring by means of the rotating ring. Further various embodiments relate to an illuminating device adopting the end cap.