Delta-like 4 (DLL4) is a membrane‑bound ligand, which belongs to the Notch signaling pathway and plays important roles in angiogenesis and vascular development. The expression of DLL4 in non‑small cell lung cancer (NSCLC) remains unclear. Therefore, DLL4 expression was detected in clinical specimens using quantum dots (QDs)‑immunohistochemistry (IHC) and lung cancer cell lines by quantitative real‑time polymerase chain reaction. The protein levels of DLL4 were decreased in the tumor tissues of NSCLC patients and lung cancer cell lines. Kaplan‑Meier analysis indicated that low expression of DLL4 predicted poor survival rate of NSCLC patients. A549 and A427 cells transfected with pCMV‑DLL4 exhibited reduced cell proliferation, migration and invasion using MTT assay, wound healing assay and Transwell assay. These data indicate that DLL4 represents a new prognostic biomarker for NSCLC, and DLL4 overexpression inhibits cell proliferation and metastasis in vitro.