Abstract: Objective To explore a possible mechanism preliminarily that soybean protein lowers serum cholesterol in rats.Methods Following 2 weeks of inducing hypercholesterolemia model successfully,femal Wistar rats were fed experimental diets containing 20% of protein each from either casein or soybean protein and either normal(0.59%)or high concentration of calcium(1.12%)respectively in a 2×2 factorial design.After 21 days.feeding,the concentration of serum total cholesterol of the rats was examined.Feces of rats were collected during the last 3 days of the trial,apparent digestibility of fat,calcium,phosphorus and mag nesium was measured.Fecal bile acid excretion was determined.Results Compared with the rats in casein group,the serum total cholesterol,digestibility of calcium and phosphor us of rats in other groups were significantly low(P<0.05).The fat dig estibility of rats in soybean protein group was lower than that in other groups.Whereas,the bile acid excretion of rats in the group fed soybean protein with high concentration of calcium was higher than that in other groups.Conclusion It indicated that the possible mechanism of soybean protein on lowering serum cholesterol in rats might relate to its non-phosphorylated status.