Abstract: Isolation of polysaccharides using isopropyl alcohol-ammonium sulfate aqueous two-phase system with ultrasonic-assisted method from sweet corncob.The main factors affecting the separation of polysaccharides from sweet corncobs were researched such as: isopropyl alcohol volume fraction,the concentration of ammonium sulfate,ultrasonic time.The response surface was designed and quadratic regression model was established with polysaccharides recovery as response values for optimizing the separation conditions.The results showed that the optimum conditions of ultrasonic-assisted isopropyl alcohol-ammonium sulfate aqueous two-phase system were isopropyl alcohol volume fraction,the concentration of ammonium sulfate,ultrasonic time was 36%,0.25 g / m L and25 min,respectively,the yield of polysaccharides under this condition was up to 98.98%. The separation of sweet corn cobs polysaccharides with isopropyl alcohol ammonium sulfate aqueous two-phase system has a good deproteinization and decolorization effect,thus,it can be used for the isolation and purification of polysaccharides from sweet corncob.