Objective To investigate the clinical features of the urolithiasis in infants who were fed with melamine contaminated powdered milk. Methods The clinical data of 165 infants aging from 50 days to 3 years(14 ± 9m) with urinary calculus who had the history of consuming melamine con- taminated powdered milk were retrospectively analyzed. All cases were treated according to the treat- ment guideline of Chinese Ministry of Health. Blood biochemical indicators (BUN, Scr, SUA) and u- rine pH value were analyzed. Thirty patients without urinary diseases or the history of consuming mel- amine contaminated powdered milk were chose as the control group. Results Eighty point six percent of the cases (138/165) had the onset under the age of 2 years, of whom 41.2% (68/165) aged from 6 to 12 months. The ratio of male to female in the 165 cases Was 2.6:1. Half of cases (49.7%) presented different clinical symptoms: dysuria(16.9%), infantile colic(14.6%), oliguria or anuria(10.9%) and hematuria(7.3%). The diameter of calculi ranged from 2mm to 16mm, of which 63.5% were between 4mm to 10mm and 9.9% were beyond 10mm After hospitalization treatment for 9 ± 5 d, clinical symptoms of all cases had vanished, and 43% cases discharged stones. Conclusions The mela- mine calculus occurred most likely in infants when fed with melamine contaminated powdered milk for over 6 months to 12 months. Nonsurgical management could get satisfactory curative effect.