Objective To improve the method in establishment of a model of renal interstitial fibrosis in rats.Methods The renal interstitial fibrosis model was established in rats by unilateral ureter obstruction(UUO).Body weight,serum creatinine(Cr) and serum urea nitrogen(BUN) level of animals from 3 groups were analyzed at the end of 1st,2nd and 3rd week.Rats were sacrificed and the pathological status of their kidneys were examined by HE,PASM and Ponceau staining at the end of 4th week.Results Cr and BUN levels in animals of the model group were significantly increased in comparison with those in sham operation group.Glomerulosclerosis,tubular atrophy,thickened glomerular/tubular basement membrane and interstitial fibrosis with inflammatory cell infiltration were observed in model group rats.A few glomerular hypertrophy and tubular dilatation were observed,too.Conclusion Model rats showing obvious renal interstitial fibrosis changes can be established by this improved technique with apparent advantage such as lower death rate,and fit for the study of renal interstitial fibrosis.