Abstract: ObjectiveTo explore the clinicopathological characteristics of echinoderm microtubuleassociated proteinlike 4anaplastic lymphoma kinase（EML4ALK）fusion genepositive nonsmall cell lung cancer（NSCLC）. Methods The clinical and pathological features of 13 cases of EML4-ALK fusion genepositive NSCLC were investigated in this retrospective analysis. Hematoxylin and eosin staining（HE）was used to evaluate the histopathological features. Immunohistochemical staining for thymidylate synthase（TS）was carried out. DNA amplification followed by direct sequencing was performed to detect the mutations in epidermal growth factor receptor（EGFR）and K-Ras. The efficacy of pemetrexed on this subtype of NSCLC were followed up. Results Thirteen cases of EML4ALK fusion gene-positive NSCLC were adenocarcinoma（male 5 cases, female 8 cases; median age 48 years; 4 cases with smoking history）. Ten cases were of acinarlike structures and 6 cases with mucus present in intracellular and extracellular. None of the tumors examined had mutations in both the EGFR and the K-Ras genes. High expression of TS were found in 3 cases and low expression levels of TS in 10 cases. Seven cases received pemetrexed chemotherapy with the disease control rate of 85.7％ and median time to progression of 5.5 months. Conclusion EML4-ALK-positive NSCLC is mostly found in young female adenocarcinoma patients who are nonsmokers. The pathological characteristics were acinar/predominant with intra／extracytoplasmic mucin. EML4-ALK-positive patients are sensitive to pemetrexed chemotherapy with low TS levels. EML4-ALK-positive cases are without EGFR or K-Ras mutation under the general condition.