Tea catechins and other flavonoids are helpful to prevent or reduce pathologic process of diabetes and chronic cardiovascular diseases. In this study, streptozotocin-induced diabetic rats were fed green tea extract for 16 weeks, and the diabetes-associated changes in Maillard-type fluorescence and carbonyl groups in the aortic collagen were compared with those occurring in the water-fed diabetic control animals. Glycated hemoglobin concentration was significantly decreased in green tea extract fed diabetic animals compared with diabetic control animals (p<0.01). Collagen-linked Maillard-type fluorescence and lipid peroxidation were significantly decreased by the green tea extract treatment (p<0.01). However, the carbonyl content was not decreased by the green tea extract treatment in the aortic collagen. The in vivo results of this study suggest that the inhibition of advanced glycation end products (AGEs) formation and lipoperoxidation in collagen is an important mechanism for the protective effects of tea catechin against diabetic complications.