Objectives : The purpose of this study was to evaluate the role of topiramate in weight gain control in bipolar patients receiving lithium carbonate and antipsychotics during their manic episode. Method: In current randomized controlled double-blind clinical trial, 46 patients with bipolar disorder in their manic episode were divided into two intervention and control groups. Both groups were treated with lithium and antipsychotics. Besides, the intervention group received topiramate and the control group received placebo . The maximum topiramate dose was 200 mg/day. The patients’ weights were assessed initially and afterwards weekly for eight weeks. Patients were evaluated using Young Mania Rating Scale (YMRS) and analysis was done by chi-square and repeated measures analysis of variance. Results: There was no statistically difference between the mean of weights in two groups at the beginning and end of the investigation (p=0.948 and p=0.254, respectively) and comparing to the beginning, there was no difference between the two groups’ weights during eight weeks of observation. Conclusion: Adjunctive treatment using topiramate (200 mg/day) was ineffective in weight gain control in manic patients receiving lithium and antipsychotics.