A new plastic microlens array, consisting of 900 lenslets, has been developed for the Shack Hartmann wave-front sensor. The individual lens is 300 μm × 300 μm and has a focal length of 10 mm, which provides the same focal size, 60 μm in diameter, with a constant peak intensity. One can improve the wave-front measurement accuracy by reducing the spot centroiding error by averaging a few frame memories of an image processor. A deformable mirror for testing the wave-front sensor gives an appropriate defocus and astigmatism, and the laser wave front is measured with a Shack Hartmann wave-front sensor. The measurement accuracy and reproducibility of our wave-front sensor are better than λ./20 and λ/50 (λ = 632.8 nm), respectively, in rms.