To discover the role of Notch3 in lung cancer and its correlation with Notch1, by reviewing the specimens of SCLC, lung squamous cell carcinoma and adenocarcinoma removed during surgery in the last two years, the expression of Notch3 in each group of lung cancer tissue and its corresponding non-tumor tissue was detected by an immunohistochemical method on the basis of the study of Notch1. The gene discussed is NOTCH3; the disease is small cell lung carcinoma.