AIM: To detect the gene expression of TGF-β2 in retinas of diabetic rats at different stages, to observe and analyze the effect of TGF-β2 on the retinas of diabetic rats, to explore the role of TGF-β2 in pathogenesis of diabetic retinopathy (DR), and to provide experiment data and experience for further clinic studies. METHODS: Sprague-Dawley (SD) rats were used and retinas were dissected. The total RNA was isolated from which the first strand of cDNA was prepared. Diabetes mellitus was induced by a single intraperitoneal injection of 60mg/kg streptozotocin (STZ) and the rats were held without insulin treatment until sacrifice. Besides, age-matched rats treated with saline were used as controls. Tail vein blood glucose was measured after 2 days and rats were considered hyperglycemic if blood glucose reading >16.7mmol/L. Animals with blood glucose level <16.7mmol/L were excluded from the study. The rats were killed at the 4th, 8th, 12th, 16th, 20th and 24th week respectively after hyperglycemic models were established. The retinas were separated and preserved in liquid nitrogen. The expressions of TGF-β2 gene mRNA were detected by reverse transcription PCR (RT-PCR). RESULTS: The RNA of rat retina was integrative enough to be used to further carry out PCR analysis. Compared with control groups, the expression of TGF-β2 mRNA in retinas of diabetic rats was up-regulated at the 4th week, but there was no statistical difference (P >0.05); it was down-regulated at the 8th week, and there was statistical difference (P<0.05); it was also down-regulated at the 12th week, and there was statistical difference (P<0.05); at the 16th week there was no statistical difference (P >0.05); it was up-regulated at the 20th week, but there was no statistical difference (P>0.05); it continued to be up-regulated at the 24th week, and there was statistical difference(P <0.05). CONCLUSION: Since the expression of TGF-β2 mRNA in retinas of diabetic rats was down-regulated at the 8th week and 12th week statistically, up-regulated at the 24th week statistically, it has obviously shown that TGF-β2 was down- and up-regulated through the period of DR. That is, its changes are diphasic with time. It may confirm that TGF-β2, with the characteristic of diphasic regulation, played an important role in DR. It is necessary to study it furthermore.