Abstract: A basal diet without adding Bacillus subtilis and four test diets containing 2×106, 2×107, 2×108 and 5×108 cfu/g of the B. subtilis were prepared to feed five groups of fish in triplicate with an initial average body weight of (4.16±0.03) g respectively. The feeding experiment was conducted in 15 re-circulating tank systems (80 L each) at a controlled water temperature of (25±0.5)℃ for eight weeks. The results showed that the weight gain of fish fed diets with B. subtilis increased significantly compared to that of fish fed the basal diet (PPB. subtilis showed no significant difference (P>0.05). Survival rates were not affected by adding B. subtilis to diets (P>0.05). Intestine protease activities of fish fed diets with B. subtilis were higher than that of fish fed the basal diet (PB. subtilis supplement up to 2×107 cfu/g, but above this level, it appeared to keep stable. The intestine amylase activity of fish fed diets with B. subtilis increased significantly (PB. subtilis supplementing appeared to have higher activity. Fish fed diets with 2×107, 2×108 and 5×108 cfu/g B. subtilis had higher hepato-pancreas protease activities than those of fish fed the basal diet and a diet with 2×106 cfu/g of B. subtilis. While the hepato-pancreas amylase activity, hepato-pancreas and intestine lipase activity were not affected significantly by dietary adding of B. subtilis (P>0.05), the body composition was not affected either. In conclusion, under the condition of this experiment, adding 2×106—5×108 cfu/g B. subtilis to fingerling black carp diet could improve fish growth and feed conversion without affecting the body composition.