To investigate the frequency of vesicoureteral reflux, and the relationship of pretransplant decreased bladder capacity and post-transplant vesicoureteral reflux in children undergoing kidney transplantation. A voiding cystourethrography was carried out in 172 pediatric kidney transplantation recipients before, and 4months after, transplantation to evaluate bladder capacity and vesicoureteral reflux. The correlation of post-transplant vesicoureteral reflux with pretransplant bladder capacity, vesicoureteral reflux in the native kidney and the method of ureteral reimplantation (intravesical/extravesical) was analyzed. Atrophic bladder was defined as having ≤50% functional bladder capacity (age in years+2)×25 (mL) or ≤150mL in patients aged >10years. Bladder capacity increased remarkably after transplantation in both post-transplant vesicoureteral reflux- group (from 180 to 253mL) and vesicoureteral reflux+ group (from 82 to 171mL). Voiding cystourethrography showed vesicoureteral reflux in 12 cases of kidney transplantation (7%; grade1: 2, grade2: 3, grade3: 7). Pretransplant atrophic bladder was an independent risk factor of post-transplant vesicoureteral reflux (P=0.004, hazard ratio 9.5). There was no difference in renal function between the vesicoureteral reflux- group and vesicoureteral reflux+ group at 4months to 5years post-transplantation. Pretransplant atrophic bladder is a risk factor of post-transplant vesicoureteral reflux in pediatric patients. However, bladder capacity can remarkably increase after transplantation, and kidney function in the post-transplant vesicoureteral reflux+ group is stable.