A method for fabricating image sensor is disclosed. The method includes the steps of: providing a substrate, wherein the substrate comprises a plurality of photodiodes; forming at least one dielectric layer and a passivation layer on surface of the substrate; using a patterned photomask to perform a first pattern transfer process for forming a plurality of trenches corresponding to each photodiode in the passivation layer; forming a plurality of color filters in the trenches; covering a planarizing layer on the color filters; and using the patterned photomask to perform a second pattern transfer process for forming a plurality of microlenses corresponding to each color filter on the planarizing layer.