Provided are a CMOS image sensor and a fabricating method thereof. The CMOS image sensor includes a device isolation layer, a plurality of photodiode regions, an interlayer insulating layer, a refracting layer, a planarizing layer, a color filter layer, and a plurality of microlenses. The refracting layer, with a higher refractive index than that of the interlayer insulating layer, is formed through the interlayer insulating layer on portions of the device isolation layer, to divide the interlayer insulating layer and give the divided portions thereof the characteristics of a waveguide.