We report a case of a 74-year-old woman with no history of HIV infection or pyothorax who presented with progressive dyspnoea. Computed tomography (CT) showed bulky pleural mass and pleural effusion associated with the right-sided pleural disease. Thoracoscopic pleural biopsy was performed and revealed the diagnosis of primary pleural malignant lymphoma. Histopathological and immunohistochemical examinations revealed that it was small B-cell lymphoma with neoplastic cells that expressed the CD-20 antigen. This case is thought to be a very rare case of primary malignant lymphoma arising in the pleura of a patient with no history of pyothorax.