Abstract: Objective: To assess the relevance of the expression of indoleamine-2,3-Dioxygenase(INDO) in non small cell lung cancer(NSCLC) and the clinical pathological parameters of NSCLC.Methods: Immunohistochemistry method was used to detect the INDO expression in 80 NSCLCs,including primary pulmonary carcinoma and lymph node metastatic carcinoma,and the tissue samples of 40 cases were screened by Western blot analysis to detect the expression of INDO in the cancer and normal tissues.The metastasis stage was defined on the basis of the results of operation,pathological test and imaging diagnosis.The correlation between the expression of INDO and the clinical pathological parameters was analyzed.Results: Immunohistochemistry showed that the INDO was present at the cytoplasm area,and the positive rate was 80.00% in the primary cancer tissue,demonstrating a great increase in comparison with the control(20.00%)(P<0.001),and the positive rate was 95.56% in the metastasis carcinoma group and 60.00% in the none metastasis group(P<0.01).The INDO expression in lymph node metastatic carcinoma was 97.78%,which was significantly higher than that in the primary ones(80.00%)(P<0.01).Conclusions: INDO is over-expressed in the NSCLC group,and is obviously related with the lymph node metastasis of NSCLC,which indicates that over expression of INDO may have a positive correlation with the metastasis of NSCLC.