A molding die has through holes composed of feed holes and slit grooves for producing honeycomb structure bodies. The slit groove is formed in at least a part of each through hole. In a method of inspecting the molding die, a light is irradiated into the feed holes side to pass through the through holes. A camera is disposed at the slit groove formation side of the molding die to photograph the amount of light output from the slit groove side. A difference in intensity of the amount of light output from the slit grooves is calculated in order to detect at least the presence of a defective slit groove having an abnormal part. In another method of repairing the defective slit groove, a modifier made of abrasive grains and clay mother material is forcedly provided into the defective slit groove in order to repair or remove the abnormal part.