An image sensor includes a substrate including a first surface and a second surface facing the first surface, a first photodiode located in a first region of the substrate and generating photocharges from light incident on the first region, a second photodiode located in a second region of the substrate and generating photocharges from light incident on the second region, and an isolation structure defining the first region in which the first photodiode is located and the second region in which the second photodiode is located, and extending between the first photodiode and the second photodiode. An area of the second region is smaller than an area of the first region, a first end of the isolation structure is coplanar with the second surface, and the isolation structure extends in a vertical direction from the second surface of the substrate toward the first surface of the substrate.