The effects of preweaning diet experience on the metabolic response of adult male rats were examined. Rats were preweaned on day 18 and were fed a high fat (HF) or a high carbohydrate (HC) diet. After age 3C1 days, each of two preweaned groups (PW) and a normal weaned group (NW) (on day 30) was fed a high fat diet (HF) or a control diet containing 2% cholesterol until 72 days of age. Animal was killed when aged 30 or 72 days and level of serum cholesterol was determined. HF group at 30 days of age had significantly higher serum cholesterol level and had more weight gain, liver weight liver total lipid and liver cholesterol than NW group or HC group. At 72 days of age, serum cholesterol level in HC group (135.61 ㎎/㎗) was double as that of NW group (72.71 ㎎/㎗), and HC group had more weight gain and epididymal fat pad than NW group. Feeding control diet during 6 week postweaning resulted in higher blood cholesterol level than HF diet feeding, but there was no difference in blood cholesterol level between H~C and NW group by feeding a control diet or a HF diet which contained 2% cholesterol. Present results indicate that metabolic systems of blood cholesterol in adult rat are affected by preweaning period and diet.