This study was designed to investigate the effect of age on the lipid metabolism in the rats fed different diets. In experiment A male Wistar rats of 5 weeks of age and of 32 weeks of age were divided into low fat diet groups and high fat-cholesterol groups. The rats were sacrificed 1 week, 2 weeks and 4 weeks after experiment begins. Also after 4 weeks. the rats in low and high fat diet groups were tube-fed 500mg of choelsterol and were sacrified 3 days later. In experiment b, male Wistar rats of 4 weeks of age and of 6 months of age were divided into 2 groups of butter and cron oil groups. And then eachgroup were divided into 2 subgroups ; meal feeding and nibbling groups . Each diet was fed for 4 weeks. In experiment A, age of the rats and experimental diets did not affect the serum cholesterol and triglycerides concentrations were higher in rats fed high fat cholesterol diet than in those fed low-fat or high -fat diets, but age of the animals had no effect on liver lipid content. The weight and cholesterol content of epidymal fat pad, however were higher in adult rats than in young ones regardless of the diets fed. When the rats were challenged with 500mg cholesterol, the rates of increase in serum and hepatic cholesterol level were higher in adult rats compared to young rats regardless of the diets . On the other hand, the rate of increase of small intestinal cholesterol content was lower in adult rats than in young rats. In experiment B, serum cholesterol and triglyceride content were relatively higher in young rats than adult ones. Stored body lipid was higher in adult rats, as judged by epididymal fat pad weight and total carcass lipid. Meal frequency and the kinds of fat in the diet did not affect the serum choelstero concentration . The serum triglyceride levels. however, was higher in butter fed rats thancron oil fed ones. The cholesterol content of live rand epididymal fat pad was lower in butter fed groups than corn oil groups for both young and adult rats, but there was no difference in liver triglycerides livel.