This experiment was conducted to examine the utilization of added dietary selenium (Se) as an immune stimulant in juvenile olive flounder, Paralichthys olivaceus. Fish averaging $4.0{pm}0.1;g$ ($mean{pm}SD$) were fed one of seven semi-purified diets containing 0.56, 1.07, 2.86, 4.56, 43.15, 90.71, or 161.74 mg of Se/kg ($Se_{0.56}$, $Se_{1.07}$, $Se_{2.86}$, $Se_{4.56}$, $Se_{43.2}$, $Se_{90.7}$ and $Se_{161.7}$, respectively) for 12 weeks, respectively. At the end of the feeding trial, the fish fed diets containing more than 43.2 mg of Se/kg showed above 90% mortality. There were no significant differences in weight gain, feed efficiency, specific growth rate, protein efficiency ratio, or hematological characteristics among the fish fed the $Se_{0.56}$, $Se_{l.07}$, $Se_{2.86}$, and $Se_{4.56}$ diets. Se concentrations of the gill, kidney, muscle and liver tissues occurred in dose-dependent manners. Alternative complement pathway activation and the chemiluminescene responses of the fish fed the $Se_{1.07}$ diet were significantly higher than those of the fish fed the other diets (P<0.05). These results indicate that the optimum dietary supplementation level of Selenium as selenoyeast could be 1.07 mg of Se/kg based on the non-specific immune responses of juvenile oilve flounder, Paralichthys olivaceus.