A 77-year-old man subacutely suffered from productive cough and low-grade fever. A chest CT scan showed small infiltration in the right lower lung and moderate pleural effusion in the right side. He was highly suspected of having tuberculous pleuritis because of increased lymphocytes and an elevated adenosine deaminase level in the pleural effusion. He did not agree to undergo diagnostic thoracoscopy; therefore antituberculous treatment consisting of isoniazid, rifampicin, and ethambutol was started. Four weeks later, Mycobacterium kansasii was confirmed in the cultured effusion; therefore he was diagnosed to have pleuritis M. kansasii. Although the side effects obliged us to change the medication, the pleural effusion gradually decreased with the combined administration of a steroid. Pleuritis due to M. kansasii is very rare; however, the clinical findings of the condition are similar to those of other mycobacteria.