An unhooking prevention structure for a spare tire carrier includes a carrier main body portion for holding a spare tire below a floor plate of an automobile; a bolt including a head portion and a shaft portion passed through the floor plate leaving the head portion on the floor plate, and the shaft portion including a male screw below the floor plate; a hook hooked onto the carrier main body portion and including a female screw screwed into the male screw of the bolt to lift the carrier main body portion by rotating the bolt around an axis; and a rotation restriction mechanism including a fitting cap attached to the head portion of the bolt so as not to rotate around the axis relative to the bolt, and preventing the hook from disengaging the bolt by prohibiting the fitting cap from rotating at a predetermined angle or more.