An image sensor includes a substrate having a first surface and a second surface, which are opposite to each other, the substrate including a unit pixel region including a device isolation pattern adjacent to the first surface and a photoelectric conversion region adjacent to the second surface, a pixel isolation pattern provided in the substrate to define the unit pixel regions, an impurity region in the unit pixel region and being adjacent to a side surface of the device isolation pattern, a gate electrode provided on the first surface, and an auxiliary isolation pattern provided between a first side surface of the gate electrode and the impurity region, when the image sensor is viewed in a plan view. A bottom surface of the auxiliary isolation pattern may be located at a level different from a bottom surface of the device isolation pattern.