An image sensor comprises a substrate having first and second surfaces opposite to each other, a fixed charge layer in contact with the second surface, an interlayer dielectric layer covering the first surface, a device isolation part adjacent to the first surface in the substrate, and a pixel isolation part in the substrate. The pixel isolation part includes a conductive pattern, a buried dielectric pattern, and an isolation dielectric pattern that is simultaneously in contact with the fixed charge layer and the interlayer dielectric layer. The isolation dielectric layer has a first thickness at a level between the buried dielectric pattern and the conductive pattern. The isolation dielectric layer has a second thickness at a level of a bottom surface of the fixed charge layer. The second thickness is different from the first thickness.