This study was carried out to investigate the effect of porphyran on enzyme activity in rats and immunity in mice. Animals were divided into 5 groups, and were given porphyran diet for 4 weeks. Porphyran was extracted from Porphyra yezoensis: Diet groups were normal diet, control diet fed high fat, cholesterol and sodium cholate, control and 1% porphyran diet (1% PD), control and 5% porphyran diet (5% PD), control and 10% of porphyran diet (10% PD). Also Balb/c female mouse were injected i.p. with porphyran extract every other day for 20 days at levels of 1%, 2% and 5%. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) activities were lower in the porphyran diet group than those in control group. Superoxide dismutase and catalase activities in liver homogenates were reduced in porphyran diet group compared to those of control group. Also, the level of liver thiobarbituric acid reactive substance (TBARS) was lower in porphyran group than that of control group. Porphyran increased IL-1 production in a dose-dependent manner, however, interleukine-2 production was reduced as the amount of porphyran increases. These results showed that supplementation of porphyran lowered antioxidant enzyme activities and has possibility of modulating immunological function.