A 59-year-old man with paroxysmal nocturnal hemoglobinuria (PNH) underwent an operation for lumbar disk herniation. He was given warfarin, aspirin, and steroid for PNH and suspected venous thrombosis. PNH is a hemolytic anemia due to an acquired red blood cell membrane defect at the stem cell level. The patient with PNH has a risk of massive hemolysis induced by stresses such as acidosis, fever, operation, trauma and overfatigue. Other main symptoms of PNH are venous thrombosis and deficient hematopoiesis. We prevented massive hemolysis by increasing the dose of steroid and avoiding acidosis, fever and dehydration during the perioperative period. Warfarin and aspirin were changed to dalteparin before operation for the prevention of venous thrombosis as well as for easy control of bleeding tendency. The perioperative course was uneventful without obvious hemolysis, venous thrombosis and unnecessary bleeding.