The cellular and nonspecific immune response of EPA were investigated in mice. ICR male mice were divided into 8 groups and received intraperiteneal injection of EPA (5 mg, 10 mg, 20 mg/kg) for 4 weeks. Cyclophosphamide (5 mg/kg) was administered i.p. 2days prior to secondary immunization. Immune responses were evaluated by hypersensitivity to SRBC(DTH), rosette forming cell(RFC), natural killer(NK) cell activity and macrophage activity. The obtanined results were as follows: As compared to normal group, 1) DTH was increased by EPA 5 mg, 10 mg administration groups. 2) RFC was significantly increased by EPA 20 mg administration group. 3) NK-Cell activity was significantly increased by EPA 10 mg administration group. 4) Macrophase activity was enhanced by EPA 5 mg administration group.