A CMOS image sensor and a method for fabricating the same are disclosed, in which light that transmits through a microlens is prevented from being beyond a photodiode region to minimize loss of incident light and to improve low illumination characteristics of the CMOS image sensor. The CMOS image sensor includes a semiconductor substrate including a transistor region and a photodiode region, a gate electrode formed on the semiconductor substrate corresponding to the transistor region, an interlayer dielectric layer formed on an entire surface of the semiconductor substrate including the gate electrode, a microlens formed over the interlayer dielectric layer to condense light, and a metal barrier formed in the interlayer dielectric layer to surround a portion of the interlayer dielectric layer corresponding to the photodiode region and to reflect light in the photodiode region that transmits through the microlens but goes beyond the photodiode region.