In previous experiment, drying efficiency of infrared and hot air dryers was investigated. On this study, drying rate of sweet potato according to different infrared interval was performed to find the optimal interval range. Steamed sweet potato was cut to a thickness of 0.5cm, the width and length were 1.5*3cm. The condition of infrared drying was 60 to 40°C, which range of interval was adjusted 5 to 20°C. Moisture content, brix, color, and texture were estimated as quality parameters. Drying rate was increased with decreasing temperature range and soluble solid contents were increased as drying time was increased, but there was no difference after 4 hours. Hardness was resulted in highest value at small temperature range and hard texture was affected by drying time. However, there were no significant differences in L, a, b value. In conclusion, small interval range of infrared was indicated highest drying efficiency and the optimal condition of drying time was 4 to 6.