Total and esterified cholesterol content was determined in the rat administered animal and vegetable proteins for 16 weeks. The cholesterol biosynthetic activity of the liver was also measured in these rats by the $acetate-C^{14}$ incorporation rate. The results obtained were as follows. (1) Serum total cholesterol content was increased by the administration of animal proteins and decreased by that of vegetable proteins. (2) Liver cholesterol content was increased by animal proteins and decreased by at of vegetable proteins. (3) Cholesterol biosynthetic activity of the liver was increased by the animal proteins and decreased by the vegetable proteins.