Mucosa-associated lymphoid tissue-derived lymphoma (MALT lymphoma) arises not only from the stomach but also from various non-gastrointestinal sites. A thirty two year old woman, suffering from breathlessness for one year, had been treated for bronchial asthma. A chest radiograph showed a mediastinum and heart transposition to the right side and emphysema of the left lung. In the thorax spiral tomography, a mass narrowing left main bronchi, five centimeters in length from the carina, was seen. A fiberoptic bronchoscopy revealed millimetric polypoid lesions those nearly totally obstructed the left main bronchi. The bronchoscopic biopsy showed a diagnosis of MALT lymphoma. She was seen for check-ups following chemotherapy but no further treatment has been carried out.