To provide a fuel tank check valve making it easy to assemble a cap to a valve element housing. This fuel tank check valve has a body tube provided with a valve element housing, a valve element, a cap, and a spring, wherein the valve element housing has a base end side frame, a tip end side frame to which the cap is mounted, and a first coupling frame connecting the both frames, the tip end side frame is provided with a retraction portion having a shape in which a circumferential part is retracted from the tip end surface thereof to the base end side frame side, the cap is formed with a notch whose circumferential part is notched, and the cap is assembled to the valve element housing so that the notch is positioned in the retraction portion.