Objective To investigate the correlation between the urinary aquaporins 2(AQP2) and urine physiological and chemical parameters in the first week after releasing ureteral obstruction on children with pyeloureteral junction obstruction (PUJO). Methods Fourteen children with congenital unilateral PUJO were included in this study. All patients presented with hydronephrosis of grade Ⅳ and Ⅴ according to Grignon's grading system. Fluid infusion after operation was under strictly control, and 24-hour urine was collected separately from hydronephrotic and contralateral non-hydronephrotic kidneys on the first, third, fifth and seventh day after operation. The urine output, osmolality, sodium and creatinine were measured. AQP2 was detected by enzyme-linked immunosorbent assay (ELISA). Results In the first week after operation, AQP2 and urine osmolality were lower, urine output and sodium excretion fraction were higher than those of the contralateral healthy kidney. Meanwhile, it had an increasing trend in AQP2 content, urine output and osmolality in bilateral kidneys. For the hydronephrotic kidney, AQP2, urine osmolality and output on the fifth and seventh day in- creased significantly compared with those on the first day (P<0. 05). And for the contralateral kid- ney, both of the AQP2 content and urine osmolality on the fifth and seventh day increased significantly compared with those on the first day(P<0.05).Sodium excretion fraction had a decreasing trend in hydronephrotic kidney. There is no statistical difference between the other parameters on different days after operation (P>0. 05). Conclusions AQP2 content of urine may be related to the change of concentration ability of collecting duct in the first week after releasing ureteral obstruction on children with PUJO.