A case of multiple myeloma with massive pleural effusion is reported. A 53 year-old previous known multiple myeloma patient vistited our hospital complaining of cough with sputum. Radiologic study revealed multiple osteolytic bony lesions and left side pleural effusion. The effusion were bloody exudates containing numerous atypical plasma cells. The tumor cells showed pleomorphism, eccentric nuclei, prominent nucleoli, perinuclear halo, multincleation, and chromatin patterns of occasional cart-wheel appearance. The cytological examination of pleural fluid established the malignant nature of the effusion with multiple myeloma.