Objective To assess the radiation dose and image quality with low-dose multi-detector row CT urography （CTU） for the evaluation of children patients with ureteropelvic junction stenosis （UJS）. Methods In this prospective study， 30 children patients with UJS underwent CTU were classified half-randomly through exam numbers into 3 groups （115 mA， 100 mA， and 75 mA）. Consecutive acquisitions including CT dose index weighted （CTDIw） and dose long product （DLP） were obtained in each patient and compared for each group. Three experienced chest radio-logists were unaware of the CT technique reviewed CT images for overall image quality using a 3-grade scale （excellent， good， and worst）. The data were analyzed using a parametric analysis of variance test and Wilcoxon’s signed rank test. Results The CTDIws of 115 mA group， 100 mA group， and 75 mA group were （7.63±0.83） mGy， （6.29±0.51） mGy， and （4.72±0.18） mGy， respectively， the difference was significant among three groups （F=36.445， P=0.000）. The mean CTDIw reduction was 38.2% in the 75 mA group as compared with 115 mA group （P＜0.001）. The DLPs of 115 mA group， 100 mA group， and 75 mA group were （173.89±29.88） mGy•cm， （145.96±26.21） mGy•cm， and （102.78±12.72） mGy•cm， respectively， the difference was significant among three groups （F=13.955， P=0.000）. The mean radiation dose reduction was 40.9% （75 mA group versus 115 mA group， P＜0.001）. The assessment of image quality was no significant difference with the same protocol and post-processing technique （Wilcoxon’s signed rank test， P＞0.05）. There was a good agreement for image quality scoring among the three reviewers （Kappa=0.736）. Conclusion Low-dose multi-detector row CTU should be considered as a promising technique for the evaluation of children patients with UJS because it could decrease radiation dose and obtain acceptable image quality.