Abstract: The sequential treatment with ultrasonic-assisted alkali extraction was applied to extract insoluble dietary fiber (IDF) from the mung bean skin and main process conditions were optimized by single-factor experiments combined with response surface methodology. The extraction rate of IDF was investigated with ultrasonic time, extraction temperature, ultrasonic powers, alkali concentration, extraction liquid-to-material ratio. The extraction rate of IDF was 66.28%±0.052%, when the extraction substance with alkali concentration 3.0 mol/L, liquid-to-material ratio 15:1 mL/g, extraction temperature 52℃, ultrasonic powers 350 W for 148 min. The results indicated that IDF could be extracted from mung bean skin effectively with this method.