Objective To investigate whether partial unilateral ureteric obstruction (PUUO) produces renal dysplasia in newborn rats. Materials and methods Left mild (in 31) or severe (in 34) PUUO was induced in 2-day-old rats by embedding quarter or two-thirds of the ureter into the psoas muscles, respectively. Sham-operated control rats (36) were assessed in parallel. Kidney morphology, renal parenchymal weight and histology were examined 24 weeks and 30 months afterward. Results There was significant pelvic dilatation in all obstructed kidneys: four kidneys were dysplastic in those severely obstructed, with a significant decrease in renal volume. There were three dysplastic kidneys after 6 months and one at 30 months. The in vitro dysplastic kidney weight was 36% of the control kidneys. Microscopy showed primitive glomerular and tubular structures. with renal parenchymal developmental disorganization and marked fibrosis. The glomeruli, tubules and collecting ducts were deficient in number and had often undergone cystic changes. Columnar tubular epithelium and peritubular mesenchymal collars were present. There was no renal dysplasia in the mildly obstructed and sham-operated rats. The parenchymal weight of the kidneys contralateral to the dysplastic kidneys was significantly higher than in the controls (P<0.001). Conclusions Severe PUUO Can produce renal dysplasia in newborn rats. However, only 12%, with severe obstruction had renal dysplasia, indicating that the cause of renal dysplasia Might also be related to other factors.