Pulmonary hamartoma is a common benign neoplasm that is usually asymptomatic and that arises in the periphery of the lung. However, when the tumor is growing without showing characteristic findings of hamartoma, such as involving calcification, fat density, and chondromatous contents in chest X-rays or computed tomography, the diagnosis is sometimes that problematic and definitive histological diagnosis should be established. We herein report a case with a massive hemoptysis 10 days after a successful transbronchial biopsy. A 69-year-old man who underwent mitral valve plasty 6 years earlier presented a left lung shadow during a routine chest X-ray. The shadow was seen to be growing by a series of chest X-rays. A week after warfarin had been stopped, a bronchoscopic biopsy was performed. No bronchial hemorrhage was observed during the procedure, and warfarin was not restarted. The patient began noticing bloody sputa once or twice a day, and 10 days after the biopsy, 400 mL of hemoptysis was suddenly disgorged. An emergency left upper lobectomy of the lung was performed, and the hemoptysis soon disappeared postoperatively. The patient is well without respiratory symptoms 36 months after the surgery.