A wire harness mounting structure for a motor vehicle door comprising a door frame and planar mounting means, detachably attached to said door frame at an internal side of its motor vehicle, having a wire harness mounted thereon and extending in a plane generally parallel to the door frame. The mounting means is either in the form of a covering board, or a combination of the covering board and an internal side board mounted between the vehicle door frame and the covering board, and, is either integrally formed with the covering board or independently, rigidly formed as in the case of an internal side board. The wire harness is terminated at the hinge mounting end of the door frame in a bundled leading-out portion which in one embodiment is fixed to the door frame by a waterproof grommet which surrounds the leading-out portion and is supported in a groove formed in the hinge mounting end of the frame at a corner portion defined by the inner side surface of the door frame and the hinge mounting end of the frame.