A method for fabricating a CMOS image sensor with a prism includes the steps of: forming a plurality of photodiodes corresponding to respective unit pixels on a substrate; sequentially forming an inter-layer insulation layer and an uppermost metal line on the substrate and the photodiodes; etching the inter-layer insulation layer to form a plurality of trenches corresponding to the respective photodiodes; depositing a high density plasma (HDP) oxide layer such that the HDP oxide layer disposed between the trenches has a tapered profile; depositing a nitride layer having a higher refractive index than that of the inter-layer insulation layer to fill the trenches; and depositing an insulation layer having a lower refractive index than that of the nitride layer to fill the trenches, thereby forming a prism, wherein the prism induces a total reflection of lights incident to the photodiodes disposed in edge regions of a pixel array.