This paper reports the fabrication of double-sided micro-lens arrays using a UV injection molding process. The apparatus for UV injection molding is designed and implemented. Because the double-sided micro-lens array is fabricated using a UV-curable resin, the molds must be transparent. An alignment system is also required to align the cavities. In preparing the transparent molds, the cavities for the concave micro-lens and the alignment marks are first machined on the aluminum block. Using electroforming and hot embossing, transparent polycarbonate (PC) molds that have cavities for the MLAs and the alignment marks are fabricated. The PC molds are mounted on the UV injection molding apparatus using a pneumatic clamp. A real-time optical alignment system that comprises a CCD and an X-Y table is used to align the marks in the upper and lower molds. After alignment, the UV-curable resin is injected into the molds using a pneumatic dispenser. When the resin is cured with UV light, a doublesided micro-lens array is fabricated. The cycle time is 45 s. The respective degrees of replication for a convex and a concave micro-lens array are 99.74% and 99.00%. The respective standard deviation values for the diameter and the height are 1.3 mu m, and 1.5 mu m. The optical properties of the doublesided micro- lens array are measured. The average effective focal length is 1.686 mm, with a standard deviation of 0.007 mm, which demonstrates good formability and uniformity. Using the fabricated micro-lens array, the 1.2 mm diameter of the original light source is reduced to a 50 mu m spot diameter. The images of an "A" pattern are complete and clear. This study demonstrates that a UV injection molding process that uses transparent PC molds can be used to fabricate a micro-lens array and other double-sided microstructures.