The aim of this study was to investigate the in vivo toxicity of di-2-ethylhexyl phthalate (DEHP), on the immune system of the rock bream, Oplegnathus fasciatus. Fish were injected twice intraperitoneally with DEHP (200, 400, and 800 mg/kg BW), and the cellularity and functional activity of phagocytes in the spleen and head kidney were measured. The number of head kidney leukocyte cells was significantly greater in fish treated with 800-mg DEHP/kg BW. Nonspecific immunity, as determined by the phagocytic index, was significantly decreased at 800-mg DEHP/kg BW in the head kidney. A significant reduction in phagocytic capacity was observed in the head kidney at ${geq}$400-mg DEHP/kg BW. Furthermore, significantly increased levels of serum glutamic oxaloacetate transaminase and glutamic pyruvate transaminase indicated a marked hepatic dysfunction in immunosuppressed fish. Total serum protein was significantly reduced at ${geq}$400-mg DEHP/kg BW; however, there were no significant changes in lysozyme activity. These results demonstrate that immune responses in the rock bream, Oplegnathus fasciatus can predict immunotoxicity at doses ${geq}$400-mg DEHP/kg BW.