Abstract: A method for fabricating a micro-lens and a mold cavity thereof and a light emitting device are provided. The method includes providing a substrate having a first surface for a plurality of micro nanometer structures to be disposed and arranged thereon. A metallic thin film layer is deposited on the first surface and micro nanometer structures of the substrate, and partially exposing the micro nanometer structures from the metallic thin film layer. Each of the micro nanometer structures is removed to form a mold cavity having a second surface so as to form a micro-lens having a micro nanometer lenticular face array, thereby enabling the light of light source passing through the micro nanometer structures to generate mass refraction. The micro nanometer structure of the present invention provides more even illumination and more extensive distribution, and the cost of material, power consumption, and manufacturing equipment involved are reduced.