In a structure for installing a fuel pump in a fuel tank, in which the fuel pump is attached to the fuel tank by clamping a flange portion of a pump case of the fuel pump between the fuel tank and a retainer fastened to the fuel tank, an interference portion is formed integrally with an inner peripheral edge of the retainer while being overhung inward in a radial direction, the interference portion being capable of interfering with any one of protruding portions when a relative position in a peripheral direction of the retainer with respect to the flange portion is set at a non-normal position, and a non-normal surface of opposite surfaces of the retainer is faced to the flange portion.