Alfalfa saponin was isolated from the roots of alfalfa(Medicage sativa L.) and incoporated at the level of 0.2% and 0.4% cholesterol-free diets and cholesterol enriched-diets. Wistar male rats weighing approximately 80g were fed with for 21 days. The serum lipids and fecal excretion lipids of the rats were determined and the result obtained are as follows. 1. Alfalfa saponin contained 36.4% medicagenic acid. 2. The feeding of alfalfa saponin increased cholesterol excretion but not bile acid excretion. 3. Alfalfa saponin showed hypocholesterolemic activity at 0.4% level in both the diets with and without cholesterol but the effect was not observed at 0.2% level in a diet. 4. It was indicated that the hypocholesterolemic effect of alfalfa saponin was associated with the decreased absorption of cholesterol from alimentary canal.