The purpose of this study was to compare the effectiveness of three common mood stabilizing drugs, Lithium, Carbamazepine and Valproate in the treatment of acute mania Of the 114 patients who participated in this study, 60 were treated with Lithium, 30 with Carbamazepine and 24 with Valproate. This study was a prospective and double blind study. The patients were assessed by GAF Scale and a manic symptoms questionnaire twice in the course of study and each time by one of the researchers. The findings indicated that 70% of Lithium group and 62.5% of Valproate group showed a good or moderate response to treatment, but only 30% of carbamazepine group responded well to treatment. The clinical symptoms showed a reduction of 75% in both Lithium and Valporate groups, and 40% in Carbamazepine group. Therefore there was no significant difference between the efficacy of Lithium and Valproate in the treatment of acute classic mania, but Carbamazepine was less effective than the other two drugs (P<0.01). However, Carbamazepine was effective in reducing the psychotic symptoms.