Heat/moisture‐treated potato and corn starch granules were observed by microscopy and X‐ray diffraction patterns were obtained. A scanning electron microscope (SEM) photograph of the cross section of the heat/moisture‐treated potato and corn starch granules showed a large hollow area about 1/3 of the diameter at the center of the starch granules and a layered structure resembling growth rings. From the X‐ray diagrams it was confirmed that heat/moisture‐treatment caused an alteration from the B‐type in the direction an A‐type structure in potato, whereas corn starch did not change and maintained an A‐type structure. The enzymatic digestibility of heat/moisture‐treated starch was found to be less resistant than that of native starch.