An image sensor includes a substrate including a first side on which light is incident, and a second side opposite to the first side, a pixel isolation pattern formed inside the substrate which defines a plurality of unit pixels, a first photoelectric conversion region and a second photoelectric conversion region arranged along a first direction, inside each of the unit pixels, and a region isolation pattern which protrudes from the pixel isolation pattern in a second direction intersecting the first direction, and defines an isolation region between the first photoelectric conversion region and the second photoelectric conversion region. A first width of the isolation region in the second direction on the first side is more than about 1.1 times a second width of the isolation region in the second direction on the second side.