A CMOS image sensor and a method for fabricating the same is disclosed, to decrease a darkcurrent generated in the boundary between a diffusion area of a photodiode and a device isolation layer, which includes a first conductive type semiconductor substrate having an active area and a device isolation area, the active area including a photodiode and a transistor; a device isolation layer formed in the device isolation area of the semiconductor substrate; a second conductive type diffusion area formed in the photodiode of the semiconductor substrate at a predetermined interval from the device isolation layer; a gate insulating layer and a gate electrode formed in the transistor of the semiconductor substrate; and a first conductive type first diffusion area formed in the semiconductor substrate of the boundary between the second conductive type diffusion area and the device isolation layer.