Abstract: Response surface methodology was applied to optimize the ultrasonic-assisted extraction technology of polysaccharides from turnip and the antioxidant activity of polysaccharides in vitro was studied. Single factor experiment was used to explore the effects of solvent-to-solid ratio,extraction temperature,extraction time and ultrasonic power on extraction yield. On this basis,the process conditions were optimized by Design-Expert 8.0.6 software for the response surface analysis. The antioxidant activity of the turnip polysaccharides was evaluated using the scavenging experiments of hydroxyl radicals(·OH). The results showed that the optimal extraction conditions were solvent-to-solid ratio of 44:1 (mL/g),extraction temperature of 57℃,extraction time of 56 min,ultrasonic power of 180 W. Under these optimal conditions,the yield of turnip polysaccharides was 65.43% and the relative error with the predicted value was 0.12%. Turnip polysaccharides had better ability to scavenge ·OH than ascorbic acid,and the half inhibitory concentration was 0.415 mg/mL. Therefore,the optimization experiment is effective and feasible,and the turnip polysaccharide has strong antioxidant activity.