Disclosed are an image sensor and a manufacturing method thereof. The image sensor includes a circuit layer on a first surface of a semiconductor substrate, a metal interconnection layer on the circuit layer, trenches formed in a second surface of the semiconductor substrate along a boundary of a pixel, and a light blocking layer in the trenches. The backside illumination type image sensor according to the embodiment has a light blocking structure at a rear surface of the semiconductor substrate, thereby improving sensing efficiency while inhibiting interference between adjacent pixels.