Objective To study the protective effect of cyclosporine A for acute renal function impairment induced by various of irrigation pressures in mild and severe hydronephrosis and to provided a reference values for clinical work during endourological procedures. Methods A total 20 rabbits were randomly divided into two groups: Mild hydronephrosis group(group M,n= 10),Severe hydronephrosis group(group S,n= 10). Both mild and severe hydronephrosis model were induced by embeding ureters into psoas. In each group, rabbits were randomly divided into 2 subgroups(M1, M2, S1 and S2)of respectively 5 rabbits.Groups M1, M2,S1 and S2 were respectively perfused with 60,100,20 and 100 mm Hg(1 mmHg= 0.133 kPa)pressure fluid.M and S groups were treated with CsA administered for one week before perfusion. The prefusion time was lasted for one hour.After that, the kidneys were harvested for measurement of super oxide dismutase (SOD)and malonaldehyde(MDA). And the change of mitochondrial membrane potential was detected by JC - 1 staining flow cytometry. Results For group M1, M2,S1 and S2,SOD were(30.11±2.23),(28.41± 2.26),(44.82±6.61),(40.31±5.21)U/mg respectively; MDA were(0.61±0.17),(0.60±0.15),(0.95 ±0.26),(0.80±0.32) nmol/mg respectively; the percentage of positive cell of expressing JC- 1 were (67.16±9.47)%,(60.75±11.89)%,(41.08±4.50)%,(42.36±3.44)% respectively. For M group, SOD, MDA and the percentage of positive cell has no significantly differences; For Sgroup, no abnormalities were observed. Conclusion CsA has a protective effect for damage due to renal perfusion. Give CsA before endosurgical procedures can effectively decrease damages induced by various of irrigation pressures. Key words: Hydronephrosis; Irrigation pressure; Mitochondrial permeability transition pore; Damage