Objective: A rare case of induced hypomania was reported. Method: Patient was a 78-year-old Indian female with squamous cell carcinoma of the nasal septum, childhood bronchial asthma and underlying bipolar disorder. Her bipolar disorder is currently in remission. She developed hypomanic symptoms after one week of initiation of montelukast sodium for treatment of acute exacerbation of bronchial asthma. Result: Her hypomanic symptoms improved after stopping usage of montelukast sodium. Conclusion: Montelukast sodium likely had induced hypomania in this patient.