This experiment was conducted to study the effects of replacement of fish meal by extruded soybean meal on growth,body composition and hematology indices of rainbow trout.Four hundred and fifty fish with initial body weights of(4.00±0.04) g were divided into 5 groups with 3 replicates of 30 fish in each replicate with a single factor completely random design.The experiment lasted for 90 days.The control group feed was formulated to contain 50% fish meal,the extruded soybean meal was pretreated by phytase as replacement protein source,each group contained 0(control group),13.60%,27.20%,40.80% and 54.40% extruded soybean meal to replace 0,20%,40%,60% and 80% of the fish meal.The result showed that compared with the control group,there were no significant difference in viscera somatic index,the major nutrients of whole body and muscles,serum biochemical indicators of the experimental groups(P0.05);with the increasing of extruded soybean meal replacement ratio,there were no significant difference in growth performance and feed utilization between control group and 20%～60% experimental groups(P0.05),the 80% experimental group was significantly different from the other groups(P0.05);the weigh gain rate(WGR),specific growth rate(SGR) and protein efficiency ratio(PER) were significantly lower than those of other groups(P0.05) and the feed conversion ratio(FCR) was increased significantly(P0.05).Based on quadratic regression analysis,the best replacement ratio of fish meal protein by extruded soybean meal was 26.90%.In conclusion,the maximum replacement ratio of fish meal protein by extruded soybean meal was 60% in the diets of rainbow trout,and the most suitable replacement ratio was 26.90%.