Objective To approach the changes of advanced glycosylated endproducts (AGEs), transforming growth factor(TGF-β1) and connective tissue growth factors(CTGF) in the lungs of experimental diabetic rats and their relationship. Methods Totally 48 male SD rats were divided into the diabetes mellitus（DM） group and the control group，with 24 rats in each group.The DM rat model was made by the injection of streptozocin (60mg/kg) into the caudal vein. The rats were killed and the lungs were taken at the end of the 4 th, 12 th and 20th weeks respectively after the models were established. The changes of AGEs,CTGF,TGF-β1 in rat lungs were observed with immunohistochemical assay and the image was analyzed. Results A great quantity of AGEs positive cells were observed in the alveolar epithelial cells, bronchial mucosal epithelium, angio-endothelial cells and smooth muscle cells of the DM rats. The average gray(AG) was lower than that of the controls（EM>P/EM><0.05） and decreased with the DM course（EM>P/EM><0.01）. In the 4_week DM rats, there were a few CTGF and TGF-β1 positive cells in the bronchial mucosal epithelium, angio-endotheliial cells and lung interstitial cells. In the 12_and 20_week DM rats, there were a great many CTGF and TGF-β1 positive cells. The AG was lower than that of the controls（EM>P/EM