Structural characteristics of resistant starch (RS) were investigated. Tuber starches, hydrolyzed with 1N HCl at 35°C for 8 hr followed by autoclaving-cooling treatment, were heated at 100°C for 16 hr after adjusting the moisture content to 20 or 30%. RS content of the tuber starches ranged from 5.4 to 22.7% depending on the source and type of treatment. Gelatinization parameters of RS isolated from partially acid-hydrolyzed starch with autoclaving-cooling followed by heat-moisture treatment (HMT) showed higher enthalpy (∆H) values and lower peak temperature (T p ) compared with non-acid-hydrolyzed RS. R values, the difference between completion and initial temperatures, and ∆H of RS increased by HMT. The X-ray diffraction patterns of potato and sweet potato RS isolated from partially acid-hydrolyzed starch with autoclaving-cooling showed distinct sharp peaks at 15, 25, 27, and 28°, which decreased by HMT.