A method for fabricating a CMOS image sensor includes: forming a gate electrode on a pixel region of the semiconductor substrate and, at the same time, forming a polysilicon pattern on a middle resistor region; forming a first lightly doped n-type diffusion region on the photodiode region; forming a second lightly doped n-type diffusion region on the transistor region; consecutively forming first and second insulating layers on the entire surface of the semiconductor substrate; removing a predetermined portion of the second insulation layer on the transistor region and the middle resistor region; forming a third insulation layer on the entire surface of the semiconductor substrate; forming sidewalls of the first insulating layer and the third insulating layer on the gate electrode and the polysilicon pattern by performing an etch-back process; and heavily doping n-type impurities in the transistor region and the polysilicon pattern.