Cladosiphon okamuranus is edible brown algae cultured commercially and massively at Okinawa coast. Dietary fiber occupying most of C. okamuranus isn't digested and absorbed by digestive enzymes of human. But it is known to prevent and treat constipation as metabolic disease. This study was to investigate the effects of dietary fiber extracted from C. okamuranus on the damage of liver and the blood cholesterol level in the high fat dietfed rats. The effects were measured by the levels of aspartate aminotransferase (ALT), alanine aminotransferase (AST), total cholesterol (TC), triglyceride (TG), low density lipoprotein (LDL) and high density lipoprotein (HDL) in sera. The levels of ALT, AST, TC, TG and LDL were significantly reduced in the C. okamuranus-treated group compared with the high fat diet group. But HDL level was markedly increased. The results showed that the dietary fiber extracts from C. okamuranus have the inhibitive effects of cholesterol biosynthesis in the high fat diet-fed rats.