Physicochemical properties on heat-moisture treatment of sweet potato starch were investigated. Starch granules of sweet potato observed by photomicroscope, polarized-light microscope and scanning electron microscope were round and polygonal. X-ray diffraction pattern was changed from Ca-pattern to A-pattern upon heat-moisture treatment. Water binding capacity was drastically increased as the moisture level was increased. The swelling power and solubility at the same temperature were decreased by heat-moisture treatment. Transmittance of 0.1% starch suspensions was increased rapidly from 65℃ in case of untreated starch and from 70℃ in case of treated starch. The starch on heat-moisture treatment was gelatinized over higher temperature range than the untreated starch.