To investigate the effect of sea tangle on macrophage activity in normal and diabetic states, 10week old ICR mice were fed control(C) and sea tangle(S) diet containing 5%(w/w) cellulose and 13.6%(w/w) dry sea tangle for four weeks, after which two thirds of mice(CD and SD) were made diabetic by intramuscular injection of streptozotocin(150mg/kg bw). At 4th day after diabetes was apparent by urinary glucose, one half of diabetic mice(CDM and SDM) were treated with metformin(500mg/kg bw) orally. Peritoneal macrophages obtained from 3%-thioglycollate treated mice were cultured in the presence of lipopolysaccaride from Salmonella abortus equi(10$mu extrm{g}$/ml) for 24 hrs and tumor necrosis factor-$alpha$(TNF$alpha$), interleukin-1$eta$(1L-1$eta$)and prostaglandin E2(PGE2) were measured in culture media. Release of IL-1$eta$and PGE2 from macrophage were increased in normal mice by sea tangle diet and had the same tedency in diabetic mice with or without metformin treatment although not statistically significant. Release of TNF$alpha$ tended to be reduced by diabetes but were not changed significantly by sea tangle diet. Fatty acid compositions of macrophage and liver phospholipids showed that diabetes reduced arachidonic acid/linoleic acid ratio and sea tangle diet appeared to increase contentsof polyunsaturated fatty acids.