A CMOS image sensor and a method for fabricating the same can ensure isolation characteristics using a shallow trench isolation (STI) process and a selective epitaxy method. The CMOS image sensor and method for fabricating the same can also reduce pixel size. The CMOS image sensor includes a semiconductor substrate, a first photodiode, a first epitaxial layer, a second epitaxial layer, a plurality of device isolation layers formed in isolation regions formed at the second epitaxial layer, a second photodiode formed between the device isolation layers, and a third epitaxial layer.