Background: Pyelonephritis can lead to renal scar. Objective: To evaluate the effects of betamethasone in preventing renal scarring in rat model of pyelonephritis. Methods: Sixty three female Sprague-Dawley rats were divided into seven groups. Group A was the control. Mannose-sensitive E coli was directly inoculated into the left kidney exposed under general anesthesia in groups C–G. Group B received normal saline. Two days after bacterial inoculation, groups C, E and F received gentamicin for 10 days. Betamethasone was injected for three days to animals in groups of D, E (2 days after bacterial inoculation) and F (5 days after bacterial inoculation). Group G received no treatment. Eight weeks after bacterial inoculation, animals were sacrificed and the volume (amount) of renal scar was determined using the stereological techniques. Results: Changes in the weight and volume of the kidneys were not statistically significant. No scar was detected in group A, but all other groups including group B with intrarenal injections showed scarring. The volume density and absolute volume of the scar in groups C–G were significantly more than group B (p<0.001), whereas they did not differ significantly from each other. Conclusion: Betamethasone and/or gentamicin, when used two days after induction of pyelonephritis were not effective in preventing renal scar.