The present study was carried out to investigate the effects of magnesium supplement levels and periods on lipid metabolism in male Sprague-Dawley rats given low protein and magnesium deficient diets. The effect of magnesium supplement levels and periods on lipid metabolism in rats given a low protein and magnesium deficient diet for 2 weeks were investigated. Serum total lipid and triglyceride contents were significantly lower in magnesium supplement group compared with magnesium deficient group. Serum HDL-cholesterol/total cholesterol ratio was significantly increased as magnesium supplement level was increased. Liver total lipid, triglyceride, total cholesterol and phospholipid contents were significantly lower in magnesium supplement group than those in magnesium deficient group. Serum ALP, GOT and GPT activities were significantly decreased in magnesium supplement group compared with magnesium deficient group. In summary, the effect of magnesium supplement on lipid metabolism and enzyme activities were significant and we can see that magnesium supplement level propered to be requirement level(400 mg/kg diet)in the other cases except serum lipid contents.