A method of inspecting a membrane-electrode assembly includes obtaining an X-ray transmission image by applying X-rays to the membrane-electrode assembly, and determining whether a foreign matter having a size equal to or larger than a predetermined value is included in the membrane-electrode assembly, according to a brightness reduction amount in each pixel of the X-ray transmission image obtained, while referring to a correlative relationship between the size of the foreign matter measured in a planar direction of the membrane-electrode assembly, and the brightness reduction amount in the X-ray transmission image.