Abstract: The water soluble dietary fiber was extracted from rice bran by ultrasonics-enzymatic method. Based on the single experiment, the extraction yield of water soluble dietary fiber as the response value, the best condition of soluble dietary fiber extraction was optimized by Box-Behnken experiment design and surface analysis. At last,the results showed that enzyme amount had the greatest impact on the extraction of water soluble dietary fiber,followed by liquid-solid ratio of rice bran and ultrasonic time,ultrasonic power affected least. The optimum extraction conditions were enzyme amount 5.3%,liquid-solid ratio 1∶24(g/m L),extraction time 5min,and ultrasonic power 415 w. Under this condition,the theory value of the extraction rate of the water soluble dietary fiber was 9.22%,the actual operation of the experiment turned out to be 9.36%.