A mobile phone lens assembly composed of 3 plastic aspheric lenses and an IR filter was designed. This lens assembly has an excellent imaging performance. Considering production and cost, the plastic lens 480R was chosen. The 1/4 in 3 mega-pixel CMOS made by Samsung was taken as the image sensor of the lens assembly, whose pixel size was 1.75μm, limiting resolution was 285lp/mm, F-number was 2.85 and FOV was 62°. Its MTF in the most of FOV at half of Nyquist frequency is higher than 0.5, RMS wavefront error is less than 0.14λ and maximum distortion is -0.2%.