A lens system including a first lens and a second lens is provided. The first lens has a first outer loop and at least a protrusiondisposed on the first outer loop of the first lens. In addition, the second lens is lodged to the first lens. The second lens has a second outer loop and at least a recess disposed on the second outer loop of the second lens. The first outer loop is leant to the second outer loop, and the protrusion is lodged to the recess. Accordingly, the first lens and the second lens have an excellent alignment precision.