We experienced very rare case of pulmonary blastoma in a 5 year old girl. She complained of right chest pain and productive cough for 3 months. With computerized tomography and echocardiography it is disclosed that huge mediastinal solid tumor is occupied to whole right thoracic cavity and compressed mediastinal structures to left and extended to left atrium. We removed the thoracic tumor and its extended intracardiac portion completely using the technique of intrapericardial pneumonectomy with cardiopulmonary bypass. Postoperatively the patient recovered without any problem and received adjuvant chemotherapy and radiotherapy. But she was succumbed 2 months later because of opportunistic pulmonary infection with pneumocystis carinii.