Objective: To explore the characteristics of clinicopathology and diagnostic criteria about pulmonary carcinosarcoma (LCS). Methods: The clinical data, histopathologic observation and immunohistochemical staining were studied in one case of lung carcinosarcoma, in order to explore its diagnosis and differential diagnosis combined with literatures. Results: Microscopic examination showed that the component of carcinoma and sarcoma was mixed each other without transitional forms. The component of carcinoma was moderately differentiated squamous cell carcinoma, and the tumor cells were nest clumps or flake. Intercellular bridges were seen with keratin pearl, occasionally. The tumor cells were pleomorphism obviously with visible nuclear fission. Conclusion: It is essential to grasp the pathological characteristics of lung carcinosarcoma to avoid misdiagnosis with raising awareness.