A capacitor, an image sensor circuit and fabricating methods are provided. The method includes providing a base substrate including a trench region and a body region adjacent to the trench region. The method also includes forming a first trench structure and a second trench structure on the first trench structure, in the base substrate in the trench region. In addition, the method includes forming a dielectric layer on a sidewall surface and a bottom surface of the first trench structure and an electrode layer on the dielectric layer in the first trench structure. Further, the method includes forming an isolation layer filling the second trench structure.