Objectives: Resistant starch（RS） escapes digestion until reaching colon and acts like dietary fiber. Recently, many studies suggest that RS, in addition to dietary fiber, may be beneficial for our health. Sweet potato (Ipomoea batatas) is very common carbohydrate source in Japanese diet. Japanese cook and eat sweet potato by boiling, steaming, baking or other cooking methods. RS content might vary when sweet potato will be cooked by different methods. Therefore, the purpose of this study was to investigate effects of cooking methods on RS andinsoluble dietary fiber (IDF) contents of sweet potato.Materials & Methods: Potatoes were cooked by three different methods (boiling, steaming or microwaving) until they reached the same degree of tenderness. The temperature of sweet potatoes was also monitored during cooking. Immediately after cooking, these samples were dehydrated and measured moisture, RS and IDF content.Results & Findings: The content of RS in raw sweet potato was 12.0%. The content of RS of boiling, steaming, and microwaving were 8.8%, 10.2% and 5.2%, respectively. The content of IDF in raw sweet potato was 5.0%, and that of boiling, steaming, and microwaving were 7.3%, 6.0% and 6.2%, respectively. RS content of steaming sweet potatoes was the highest among three different cooking methods. This result might be related with cooking temperature, cooking time or moisture content of sweet potatoes. The contents of IDF among raw and three cooking methods were a little different. The content of IDF by boiling was higher than that of raw sweet potatoes. It might be included partial RS and measured as IDF.