A patient who has multiple lung masses with a history of malignancy in organs other than the lung is more likely to be diagnosed with metastatic rather than primary lung cancer. Rarely, metastatic cancer can coexist with primary. We experienced a case of concurrent diagnosis of primary small cell lung cancer and pulmonary metastasis of uterine malignant mixed M$ddot{u}$llerian tumor (MMMT). The patient was a 52-year-old female with femur fracture and multiple lung masses with a history of an operation for uterine MMMT. The small cell lung cancer was diagnosed by bronchoscopic biopsy. The central lung mass decreased after chemotherapy for small cell lung cancer but multiple peripheral masses increased. A percutaneous biopsy for one of peripheral masses revealed metastatic uterine MMMT. We suggest that we have to consider the possible presence of concomitant malignancies of different origins in one organ especially with patients who had a history of malignancy in another organ.