Purpose To assess the expression of DLL4 in non-small cell lung cancer ( NSCLC) patients and to determine its associa-tion with clinicopathological parameters and prognosis. Methods DLL4 expression was evaluated in NSCLC tissues and adjacent non-cancerous normal lung tissues from 89 patients undergoing surgical treatment by immunohistochemistry. Results DLL4 had high ex-pression in 52 of 89 cases of NSCLC (58. 4%), which was significantly higher than that in adjacent non-cancerous lung tissues (P<0. 05). Moreover, DLL4 overexpression was significantly correlated with TNM stage (P=0. 010 78). Kaplan-Meier survival analysis showed that the overall survival times in patients expressing DLL4 in NSCLC were shorter. Conclusion High level of DLL4 expression is significantly correlated with NSCLC progression and unfavorable prognosis. Thus, DLL4 expression may be used as a clinical param-eter for predictive prognostication of NSCLC patients.