Objective　To investigate the protective role of glycyrrhizin on experimental obstructive nephropathy in rats. Methods 　The model of obstructive nephropathy was induced by unilateral uretera l ligation in rats and the animals were sacrificed at 12 h and 3,14,28,56 d resp ectively after operation. Specimens were taken from the cortex of kidney. In re nal stroma, routine morphological examinations and counts of karyocyte were made , the expression of collagen type Ⅰand type Ⅲ were also detected by immunohist ochemical staining,then, semi-quantified by EIG image analysis system. Results　 A progressive fibrosis was observed in renal stroma of the mod el. 12 h after operation, counts of karyocyte increased markedly i n renal stroma in groups of treatment and pretreatment with glycyrrhizin compar ed with that in sham-operation group（P<0.05）,and decreased distinctly compared with that in saline treated group（P<0.01）, but no significant di fference was found between treatment group and pretreatment group（P>0.05） ;3 d after operation, in group treated or pretreated with glycyrrhizin. The e xpression of collagen type Ⅰ increased markedly compared with that in sham-o peration group（P<0.01） in renal stroma, but decreased notably compare d with that in saline treated group（P<0.01）,while, there was not any diffe rence between treatment group and pretreatment group（P>0.05）. The expressi on of collagen type Ⅲ in renal stroma was almost the same as that of coll agen type Ⅰ. Conclusion　Glycyrrhizin has some therapeutical bu t no preventive effect to experimental obstructive nephropathy in rats.