This study was performed to investigate the effects of the chitosan oligosaccharide administration on the improvement of the lipid compositions, blood glucose and enzyme activities in the serum of hypercholesterolemic rats fed the experimental diets for 5 weeks. Concentrations of total cholesterol, atherosclerotic index, LDL, LDL-cholesterol, free cholesterol, cholesteryl ester ratio, triglyceride (TG), phospholipid (PL) and blood glucose in serum were higher in the hypercholesterolemic group (group CW) and cholesterol+chitosan oligosaccharide administration group (group CCW) than those in the control group (group BW, basal diet+water). But the concentrations of total cholesterol, atherosclerotic index, LDL, LDL-cholesterol, free cholesterol, cholesteryl ester ratio, TG, PL and blood glucose in serum were lower in the group CCW than those in the CW, whereas the ratio of HDL-cholesterol concentration to total cholesterol and HDL-cholesterol concentration in the group CCW were higher than in the group CW. The activities of alkaline phosphatase (ALP) and aminotransferase (AST, ALT) in serum were lower in the group CCW than in the hypercholesterolemic group CW. From the above results, it was suggested that chitosan oligosaccharide administration was effective in the prevention and improvement of the lipid level, blood glucose and enzyme activities in serum of hypercholesterolemic rats.