The cholesterol metabolism in male Wistar strain rat was studied on the biosynthesis of steroid hormone. 3H-cholesteryl ester was completely formed by 5 hours after the 3H-cholesterol administration from tail vein, and were recoginzed the metabolites from 3H-cholesterol in the adrenals, liver and serum after 2 hours. The steroid hormones from 3H-cholesterol observed maximum conversion at 5 hours. The metabolic processes were studied in rat bearing Walker carcinoma. The cholesterol conversion to steroid hormone in vivo in tumor bearing rat was elevated twice than the normal.