Pulmonary blastoma is a primary lung tumor consisting of a mixture of immature embryonal-like mensenchymal and epithelial components and in some areas resemble embryonal lung tissue of up to 3-4 months gestational age. The tumor was first described in 1945 by Barrett and Barnard and again in 1952 by Barmard, who named it an embryoma of the lung which resembled fetal lung histologically, with glandular structures lined by non-ciliated epithelium and a surrounding stroma resembling mesenchyme. In 1961 Spencer renamed them Pulmonary blastoma as he believed they represented neoplasms similar in pathogenesis to nephroblastoma. The prognosis of these tumors is poor, and the clinical course is not readily predicted from histological appearance. Untill now, more than one hundred cases have been reported in the literature in the word and there is no report in Korea. We report a case of biphasic pulmonary blastoma, which ruptured spontaneously, in a 31-year-old young man who was presented as sharp pain under the right subscapular area.