A 69-year-old man was diagnosed as having syndrome of inappropriate secretion of antidiuretic hormone (SIADH) (serum sodium: 113 mEq/L) 13 days after a right upper lobectomy due to squamous cell carcinoma of the lung (pT1N0M0, stage IA) whereas the preoperative serum sodium level was nearly normal. He had undergone pleurodesis by instillation of OK432 at 2 and 5 days after surgery for prolonged air leakage. Since other possible causes of SIADH, such as residue of lung cancer, pulmonary infections, brain disorders, or known causative drugs were ruled out, the SIADH in this patient was likely associated with pleurodesis by the use of OK-432. A review of similar cases reported suggests that it is important to be aware of the possibility of severe hyponatremia due to SIADH after chemical pleurodesis.