A 59-year-old man took mefloquine (antimalarial drug), total dose of 1,000 mg, to prevent malaria before and during traveling to South Africa. Three weeks after the first administration, he was admitted complaining of fever and dyspnea. Chest HRCT showed ground-glass opacities and consolidation in both lung fields. Withdrawal of mefloquine and treatment with corticosteroid resulted in improvement of the clinical findings. From the clinical course, we considered this case to be mefloquine-induced pneumonia. Mefloquine may have caused pulmonary toxicity.