This paper presents a simple and effective method to fabricate a polydimethyl-siloxane (PDMS) microlens array with a high fill factor, which utilizes the UV proximity printing and photoresist replication methods. The concave microlens array mold was made using a printing gap in lithography process, which utilizes optical diffraction of UV light to deflect away from the aperture edges and produces a certain exposure in the photoresist material outside the aperture edges. This method can precisely control the geometric profile of concave microlens array. The experimental results showed that the concave micro-lens array in photoresist could be formed automatically when the printing gap ranged from 240 micron to 720 micron. High fill factor microlens array can be produced, when the control pitch distance between the adjacent apertures of the concave microlens array was decreased to the aperture size.