The present study was conducted to investigate the effects of dietary -1,3-1,6-glucan (BG) from Schizophyllum commune on the innate immune response in cobia (Rachycentron canadum). Cobia (50-80 g) were fed a basal diet and supplemented with either 0 (control group) or 0.5% BG (glucan group) for 60 days. The superoxide anion (O2-), superoxide dismutase (SOD) concentration and lysozyme activity were analyzed at days 0, 1, 3, 6, 12, 20, 30, 40, 50 and 60. The results showed that the concentration of O2- and SOD and activity of lyszoyme in cobia at BG group was higher (p < 0.001) than those of the control group. They attained the highest levels at day 12, 20 and 24 after feeding, respectively. However, the concentration of O2- on day 30, SOD on day 40 and activity of lysozyme on day 40 of the fish at BG group, dropped back to the same levels as the control group (p > 0.05). The results in this study showed that oral administration of 0.5% BG for 6 days enhanced immunity of the cobia, but prolonged use of BG would not increase the immunity of the cobia. Care therefore must be taken to maximize its effectiveness with suitable period.