An exemplary method for fabricating a mold core includes the following steps. First, an ultraviolet (UV) transmitting glass substrate is provided. Second, a photo resist layer is formed on the substrate. Third, the photo resist layer is exposed under a UV light and developed to form a plurality of spaced through holes therein. Fourth, the areas of the surface of the substrate under the through holes are etched to form a plurality of cavities. Fifth, each cavity is filled with a light-curable material, and the photo resist layer is removed. Sixth, the light-curable material is solidified to form a light-cured material block in each cavity. Lastly, the light-cured material block in each cavity is machined using an ultra-precision machine to form a molding surface of the light-cured material block. Thereby, the mold core with a plurality of the molding surfaces is obtained.