A 60-year-old man with exertional dyspnea and massive right pleural effusion was admitted to our hospital. Based on the deposition of amyloid light chain (AL) proteins in the gastric mucosal layer and the absence of myeloma cells in the bone marrow, we diagnosed the patient with AL amyloidosis. The pleural effusion was bloody, exudative, and composed predominantly of lymphocytes. A right parietal pleural biopsy using a Cope needle was performed. We identified amyloid depositions in the parietal pleural tissue, confirming the diagnosis of pleural amyloidosis as the etiology of the right pleural effusion. The patient's dyspnea improved after drainage of the pleural effusion, but the right lung showed inadequate expansion, suggestive of an unexpandable lung. Despite seven courses of chemotherapy, the unexpandable lung and right pleural effusion persisted; however, the patient's dyspnea did not recur.