The sweet potato is recognized as a health-promoting food, owing to its richness in functional components such as dietary fiber; however, only a few studies have been conducted on resistant starch (RS) levels in the sweet potato. Now, the sweet potato is expected to have potential as a renewable resource for bio-ethanol production. The enzymatic digestibility of raw starch appears to influence the conversion rate of starch to sugar in the first step of ethanol production. In this study, the RS content of gelatinized starch, digestible starch (DS) content of raw starch and other starch properties were investigated using 21 sweet potato cultivars and lines to assess varietal variations and to estimate relationships among these starch properties. The RS content of gelatinized starch ranged between 1.8 and 9.5%. The DS content of raw starch ranged between 69.3 and 98.3%. Analysis of variance indicated that the varietal differences were significant at the 0.1% level for both the RS content and the DS content. Sweet potato starches with high amylose content and low paste viscosity showed high RS content of gelatinized starch. Starches with low pasting temperature and slow retrogradation showed high DS content of raw starch. A new breeding line, Kyukei 03284-156, contained a unique starch having the highest RS content, highest amylose content, lowest paste viscosity and abnormal granule morphology. The results of this study are expected to provide useful information to food industries that utilize sweet potato starch and to breeders that attempt to improve the RS and DS contents in sweet potato cultivars.