Background: Urinary tract infection in children may cause renal scar formation, which can be prevented by early and appropriate treatment. Recent studies showed that single daily injection of gentamycin can produce best effect without increasing the side effects. The aim of this study was to evaluate the rate of renal scar formation when new regime (every other day gentamicin injection) used for treatment of urinary tract infection. Methods: Forty eight Sprague Dawley rats were infected by inoculation of 0.1 ml Uropathogenic E.coli suspension (109/ml) to their left kidneys. The rats were divided into four groups after 24 hours. Gentamicin was administrated intraperitoneally at dosages of 10mg/kg (daily), 10mg/kg every other day or 20mg/kg every other day to the first three groups. The fourth group did not receive any antibiotic. Renal scar formation was evaluated by histology and responses were evaluated by counting colony forming units (CFU)/ml of homogenized kidney tissue and percentage of sterile kidneys. Results: Evaluation of all sections showed that 0-30% of interstitial tissues had scar formation. The results showed no significant difference in scar formation between the first three groups, but showed mild to moderate scar formation in the fourth group. Conclusion: It was concluded that 10mg/kg or 20mg/kg of gentamicin usage in every other day interval dose did not increase the risk of renal scar formation while it had appropriate efficiency.