A fuel tank structure is obtained that can prevent or suppress excessive stress concentrating at fixed portions of a separator and an inner wall of a fuel tank main body. A separator for reducing flow noise of fuel is disposed at an interior of a fuel tank that accommodates fuel. Projecting portions that serve as fixed portions that are fixed at two or more places to an inner wall of the fuel tank, are provided at the separator. Deformation portions that allow deformation of the separator are formed between the projecting portions at the separator.