The most prevalent disease in the jaw is the chronic inflammatory periapical lesion. The lack of impact of calcium hydroxide dressing on healing results suggests that more effective inter-appointment dressings should be developed. Simvastatin is one of the most widely used pharmaceuticals in the world todayas means of combating high cholesterol. Simvastatin's osteopromotive capabilities is being studied, howeverits effect on healing of periapical lesions remains unclear.Materials and methods: Periapical lesions were inducedin 64premolars in four Mongrel dogs. Dogs of one group were injected through the root canals with 2.5mg/ml simvastatin, while dogs of another group were injected with 5mg/ml simvastatin. Dogs of the control group were not injected. The animalswere sacrificed after 2 and 4weeks.Bone formation was evaluated by H&E stain, Masson-Goldner trichrome stain and osteopontin immunostain. Area percent for Masson-Goldner trichrome andosteopontinstainwas calculated. Results:The area percent of Masson-Goldner trichrome and osteopontin expression were enhanced by the dose and time of exposure to the drug. Conclusion:Although, the most important part of treating apical periodontitis is a full root canal therapy, howeversimvastatin improved the efficacy of this procedure.