This study was designed to investigate the effect of dietary Platycodon grandiflorum on plasma glucose and lipid metabolism in $KK-A^y$ mice and STZ-induced diabetic rats. Both plasma triglyceride and plasma cholesterol levels in STZ-induced diabetic rats were significantly decreased by dietary Platycodon grandiflorum feeding for 4 weeks compared to those of control rats, but there were no marked differences in $KK-A^y$ mice. However, for plasma glucose values, Platycodon grandiflorum feeding resulted in a significant decrease in both STZ-induced diabetic rats and $KK-A^y$ mice. Also, dietary Platycodon grandiflorum slightly decreased the postprandial glucose level at 30 and 60 mins during oral glucose tolerance test in $KK-A^y$ mice. Although there was no statistical significance, the fasting plasma insulin levels of Platycodon grandiflorum dieted $KK-A^y$ mice tended to decrease when compared to that of control mice. Therefore, the present results suggested that dietary Platycodon grandiflorum may have a beneficial effect on preventing hypercholesterolemia and hyperlipidemia.