Few cases of lung mucoepidermoid carcinomas with anaplastic lymphoma kinase (ALK) fusion have been reported. A 35-year-old woman was found to have an abnormal chest X-ray. A tumor and obstructive pneumonitis in her left upper lobe was detected using computed tomography (CT). She was admitted to our hospital, and was diagnosed with mucoepidermoid carcinoma by transbronchial biopsy. Left pneumonectomy and lymphadenectomy were performed for lung mucoepidermoid carcinoma and a mediastinal lymph node metastasis (pT2aN2M0, stage ⅢA). Postoperative radiotherapy (50 Gy) to the mediastinum and chemotherapy were performed followed by several radiotherapies for cervical and mediastinal lymph node and right ischium metastases. Since then, further radiotherapy was impossible. However, we detected ALK fusion in the resected specimen and the cancer responded to alectinib hydrochloride.