Extract: The effect of Spirulina on serum lipids was studied in 30 healthy male volunteers who had mild hyperlipidemia or mild hypertension through the screening test of applicants. Subjects were divided into two groups (A and B); group A subjects were given 4.2 grams of Spirulina per day for eight weeks and group B subjects were given the same amount of Spirulina for the first four weeks and for the next four weeks, they were observed without giving the agent. Total serum cholesterol was reduced significantly by giving Spirulina and when medication was discontinued in group B, it returned to baseline. The reduction was more marked in hypercholesterolemic subjects and the subjects who were taking higher amount of cholesterol. While HDL-cholesterol showed no significant changes, a slight increasing tendency was observed. There were no changes in serum triglyceride and body weight. No adverse effects were observed. Spirulina, which is at present used as a highly nutritious food, has been proven through this experiment to have serum cholesterol reduction effect.