Background and Aim: The pain after root canal treatment is one of the main problems for patient and dentist. Various drugs were studied for alleviating the pain after treatment. The purpose of this study was evaluation of various medication methods on the incidence of post treatment endodontic pain in necrotic teeth.Methods & Materials: In this controlled double blind clinical trial, 120 patients with single canal teeth and necrotic pulps were selected. The patients were divided into six groups and randomly received drugs in one of the following ways: Group A, 2gr Amoxicillin one hour before treatment. Group B, 2gr Amoxicillin plus 4mg Betamethasone one hour before treatment. In group C, 2gr placebo (control group) one hour before treatment Group D, 500 mg Amoxicillin immediately after treatment and continued every 8 hours for 4 days. Group E, the same treatment as group D was performed expect that, 4mg Betamethasone was added to Amoxicillin. Group F, the same treatment as group D was performed, but placebo was used instead of Amoxicillin.Root canal therapy was accomplished with step back technique and lateral condensation method. Evaluation of incidence of pain was recorded 6, 12,24,48 and 72 hours after treatment. Data were analyzed by Kruskall-wallis and Mann-whitney tests.Result: The results of this study in various intervals showed that there was no significant difference in the incidence of post treatment endodontic pain between those patients who received Amoxicillin or Betamethasone (A,B,D, E,F) and those who used placebo (control group C, F). Most of patients that had severe pain received placebo (C and F groups).Conclusion: Oral administration of corticosteroids plus antibiotic in cases with necrotic pulp did not significantly reduce post treatment endodontic pain.