An image sensor can include a plurality of photodiodes and a plurality of transistors formed in a semiconductor substrate; a first interlayer insulating layer formed over the semiconductor substrate; a plurality of metal lines formed over the first interlayer insulating layer, electrically connected with the photodiodes and the transistors; a plurality of interlayer insulating layers including an upper interlayer insulating layer and a lower interlayer insulating layer formed over the semiconductor substrate including the metal lines, wherein refractive indexes of the upper interlayer insulating layer and the lower interlayer insulating layer are different from each other; a plurality of color filters formed over the plurality of interlayer insulating layers and which correspond to the photodiodes, respectively; a planarization layer formed over the semiconductor substrate including the color filters; and a plurality of microlenses formed over the planarization layer and which corresponds to the color filters, respectively.