This study was performed to observe the effects of dietary fat levels and sources on lipids contents and cellularities of liver, brain, and adipose tissue of early weaned rats. Male Sprague-Dawley rats were prematurely weaned from postnatal 17th day with the experimental diets differ in fat levels : low(5%), medium(10%), high(20%) and fat sources : butter, soybean oil, butter＋ soybean oil. On the postnatal 29th day, contents of total lipid, triglyceride, cholesterol and phospholipid of serum, liver, brain and adipose tissue were determined, and DNA was determined to assess the cell growth. Rats early weaned fed high fat diet showed lower total lipid and triglyceride levels in serum and liver than those fed medium or low fat diet Rats early weaned fed high fat diet had adipocytes of fewer number, but larger size than those of rats fed low or medium fat diets. Rats early weaned fed soybean oil diet had more adipocytes thu those fed butter diet. Rats normally weaned to commercial chow diet showed lower total lipid, triglyceride, and cholesterol levels in serum and liver, had fewer adipocytes than all early weaned rats except for rats fed high fat-butter diet. These results suggest that high fat-butter diet is ideal weaning diet at early weaning.