Ctenopharyngodon idellus were fed with basal diet supplemented with 0(Ⅰ),1×108(Ⅱ),3×108 (Ⅲ),5×108 cfu/g(Ⅳ) Bacillus spp.respectively for 30 days.Feces was collected to detect apparent digestibility of feed nutrients.The apparent digestibility of dry matter,crude protein and crude lipid in Ⅰ group was significantly lower than the other treatment groups (P<0.05).Quadratic curve equation was the best to fit the relationship between dosages of Bacillus spp.and apparent digestibility of nutrients.Protease activity of the mid-gut in Ⅱgroup and the hepatopancreas inⅡ,Ⅲ groups increased significantly compared with Ⅰ group (P<0.05).Amylase activity of the fore-gut and hind-gut in Ⅱgroup increased significantly compared with Ⅰ group (P<0.05).Lipase activity of the hind-gut in Ⅱ,Ⅲ group increased significantly compared withⅠgroup (P<0.05).After feeding for 60 days,the similar results appeared.Two-way analysis of variance showed that protease activity of the mid-gut,hind-gut and the hepatopancreas,amylase activity of the fore-gut,mid-gut and hind-gut,lipase activity of the mid-gut and hind-gut were all significantly affected by the additional doseages of Bacillus spp.( P<0.05).Protease activity and amylase activity of the hepatopancreas were significantly affected by feeding days (P<0.05).