We encountered a rare case of a 72-year-old woman with an undiagnosed intrapelvic cystic mass, who presented with a smooth surfaced endobronchial tumor obstructing the orifice of the right lower lobe bronchus on a bronchoscopic examination. She had a prior history cervical cancer and adenocarcinoma in the right middle lobe lateral segment of her lung for which she had undergone radiation therapy. The tumor was diagnosed as an endobronchial sarcoma by the histopathology findings and immunohistochemistry. It was unclear if the tumor was a primary sarcoma of the lung or a metastatic lesion of an intrapelvic cystic mass because she refused a diagnostic exploratory laparotomy. Two months later, obstructive pneumonia of the right lower lobe with parapneumonic effusion developed with fever above 38.5℃ for 10 days. After recovering from pneumonia, she was followed up regularly in the outpatient clinic without any specific treatment. One year later after treating the obstructive pneumonia, the follow-up bronchoscopy revealed complete SR of endobronchial sarcoma. It is believed that the obstructive pneumonia accompanied by fever above 38.5℃ for 10 days might have played a role in this SR.