Effects of various concentrations of Scutellaria baicalensis (SB) extract in the diets on growth, body composition, serum chemistry and challenge test of far eastern catfish (Silurus asotus) were determined and compared to commercially available immune enhancer. Eight experimental diets were prepared in triplicate: Con diet without supplementation of SB and SB-0.25, SB-0.5, SB-1, SB-2, SB-3 and SB-5 diets containing SB at the concentrations of 0.25, 0.5, 1, 2, 3 and 5%, respectively. In addition, 0.1% commercial product of immune enhancer was included into the diet (CP). At the end of the 8-week feeding trial, ten externally normal fish from each tank were infected by Vibrio anguillarum and Streptococcus iniae. No significant difference in weight gain of fish was found. Feed consumption, feed efficiency ratio and protein retention of fish was not affected by the experimental diets. Cumulative mortality of fish fed the Con diet was higher than that of fish fed the all other diets since 10 and 25 days after V. anguillarum and S. iniae infectionm 5. Results of this study indicated that dietary inclusion of SB extract was effective to improve survival of fish after V. anguillarum and S. iniae infection, but the various concentrations of SB did not affect fish performance.