Objective To study the scanning techniques of low-dose CT urography (CTU) and post-processing in children with hydronephrosis. Methods From September 2011 to May 2012, a total of 43 children with hydronephrosis, aged from 4-month-old to 13-year-old received CTU in our hospital. First, the abdominal plain CT scan was implement, then 43 cases were divided into three degrees according to degrees of hydronephrosis, mild, moderate and sever. Then CTU delay scan program was conducted according to different groups, renal excretion period of mild group delayed (5~10) min, moderate group delayed (30~90) min, severe group delayed (3~5) h. After scanning, the multiplanar reformation (MPR) and volume rendering (VR) for each case were carried out, with the original data of renal excretion period images on the post-processing workstation. Post-processing image rating score were measured by two physicians. The study protocol was approved by the Ethical Review Board of Investigation in Human Being of West China Second University Hospital. Informed consent was obtained from all participates. Results The degrees of hydronephrosis were below, 20 cases for mild group (46.51%), 11 cases for moderate group (25.58%), 12 cases for severe group (27.91%). The highest average score of post-processing CTU image was mild group, with the highest satisfaction of diagnosis (80.00%); and severe group with the minimum of images average and the lowest percentage of the appraised image (29.2%); the difference between mild group and severe group was statistically significant(χ2=17.599, P<0.001). Consistency test which was measured by two physicians was excellent (κ value was 0.811). Conclusions Low-dose CTU can provide accurate diagnostic basis for pediatric patients with hydronephrosis and surgical treatment. Key words: spiral CT; urography; child; hydronephrosis