Objective: To assess the diagnostic value of dual energy CT for lymph node metastasis in patients with non-small cell lung cancer (NSCLC).Methods: Forty NSCLC patients, including 15 cases of squamous cell carcinoma and 25 cases of adenocarcinoma, underwent dual energy CT examination in pre-contrast and venous phase contrast scans, then the CT attenuation value of the lung cancer lesions and 85 mediastinal enlarged lymph nodes (the short diameter ≥ 5 mm, 53 metastatic and 32 non-metastatic) were measured at different energy levels (40-190 keV, spacing 10 keV) in venous phase contrast. CT spectral curves of the lung cancer lesions, hilus pulmonis and mediastinal enlarged lymph nodes were produced automatically, through comparing their CT spectral curves slope to judge whether or not the lymph nodes were metastatic. Receiver operating characteristic (ROC) curve was used to evaluate the efficiency of CT spectral curve in diagnosis of lymph node metastasis.Results: The CT spectral curves slopes of the lung cancer, metastatic lymph nodes and non-metastatic lymph nodes were 1.10±0.11, 1.08±0.07 and 1.54±0.17, respectively. There was no significant difference in curve slope between metastatic lymph nodes and lung cancer (t=-1.32,P>0.05); while there was significant difference between non-metastatic lymph nodes and lung cancer (t=-2.58,P<0.05). The CT spectral curve slope ratios of metastatic and non-metastatic lymph nodes to lung cancer were 0.98±0.05 and 1.40±0.12, respectively (t=-2.86,P<0.05). ROC curve showed that taking CT spectral curve slope ratio of 1.15 as cut-off value for the diagnosis of metastatic lymph nodes, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 81.1%, 87.5%, 91.5%, 73.7% and 83.5%, respectively.Conclusion: Dual energy CT is of value in improving the diagnostic accuracy of lymph node metastasis in NSCLC patients before treatment.