Abstract: A compact 2X optical zoom lens system for mobile phones was designed with ZEMAX. The system consists of 4 plastic aspheric lenses and an IR filter. The limiting resolution is 285lp/mm, which matches the CMOS image sensor of 1.75m pixel size. In the whole field of view (FOV), the RMS raidus is less than airy disk and the maximum distortion is less than 3%, the MTF at the half Nyquist frequency (285pl/mm)of CMOS in most part of the FOV were greater than 0.5,and the length of the optical zoom lens system is less than 9.2mm. It is compact in structure, high in resolution and low in cost, which meets the zoom lens system requirements of mobile phones.