Abstract: Optimized technology for preparing soluble dietary fiber from extruded soybean residue was studied by the central composite rotatable design with four variables of the ratio of liquid to solid, temperature, time and alkali concentration. The yield of soluble dietary fiber was the evaluation index. The results indicated that the effect order of four factors on the yield of soluble dietary fiber was as follows: alkali concentration, ratio of liquid to solid, temperature and time. The canonical analysis revealed that the optimal conditions for preparation of soluble dietary fiber were: ratio of liquid to solid 26∶1, temperature 89℃, time 68 min and alkali concentration 1.12%. Under optimal conditions, the predicted yield of soluble dietary fiber from extruded soybean residue was 33.96%, whereas, the experimental yield of soluble dietary fiber was 34.12%. The RSM-predicted yield and the experimental yield of soluble dietary fiber were not significantly different from each other. The results showed that the empirical model developed by response surface methodology was adequate to describe the relationships between the factors and response values. Under optimal conditions，the yield of soluble dietary fiber from extruded soybean residue (34.12%) was significantly more than that from soybean residue (13.51%).