A 72-year-old woman developed left pneumothorax 14 months after the first operation of a gingival carcinoma. The chest X-ray films and computed tomographic scans on admission revealed left pneumothorax and 2 lesions with a thin-walled cavity in the upper lung field. They seemed to be pulmonary metastasis from a carcinoma of gingiva and one of them ruptured into the pleural cavity. As airleak continued after tube thoracostomy, wedge resections of 2 lesions were performed through thoracotomy. Postoperative histological examination revealed that both of the lesions were moderately differentiated squamous cell carcinoma and they were the same histological findings as the gingival carcinoma excised previously. Pulmonary metastasis from a carcinoma of gingiva is rare, while it may be thought 1% of metastatic lung tumors. And also pulmonary metastasis is unusual cause of pneumothorax, especially without chemotherapy for it. We reported the very rare case of pneumothorax due to pulmonary metastasis from a carcinoma of gingiva.