Abstract: An image sensor structure including a substrate, a pixel structure, and a deep trench isolation (DTI) structure is provided. The substrate includes a first side and a second side opposite to each other. The pixel structure includes a transfer transistor, a light sensing device, and a floating diffusion region. The transfer transistor includes a first gate. The first gate is disposed on the first side of the substrate. The light sensing device is disposed in the substrate and is located on one side of the first gate. The floating diffusion region is disposed in the substrate and is located on another side of the first gate. The DTI structure extends into the substrate from the second side of the substrate. The top-view pattern of the floating diffusion region does not overlap the top-view pattern of the DTI structure.