An image sensor includes a substrate, a photosensitive unit, a first grid and a color filter. The photosensitive unit is located within the substrate. The first grid is located above the substrate, and the first grid has a first portion and a second portion above the first portion, wherein the second portion has a rounded top surface extending from a sidewall of the first portion of the first grid. The color filter is located above the photosensitive unit and in contact with the rounded top surface of the second portion of the first grid.