A 65-year-old woman, treated with prednisolone (5 mg daily) for rheumatoid arthritis, visited our hospital because of right chest pain. Chest CT showed small nodular shadows in the right lung accompanied with right pleural effusion. A pulmonary Mycobacterium gordonae infection was diagnosed, since M. gordonae was identified twice from her sputum. She was treated with rifampicin, ethambutol and streptomycin for two months, and then streptomycin was replaced with clarithromycin. Three months after the initial treatment, M. gordonae was eradicated from her sputum. Pleural puncture revealed bloody, exudative, lymphocytotic pleural effusion, but no malignant cells were identified. Although pathological diagnosis by thoracoscopic pleural biopsy could not be performed, it is likely that the pleural effusion was associated with the pulmonary M. gordonae infection in the present case.