Abstract Background The purpose of this study was to evaluate the diagnostic value of dual-energy computed tomography (DECT) in detecting lymph node (LN) metastasis in patients with colorectal cancer. Methods Data from 81 LNs from 28 patients with colorectal adenocarcinoma were retrospectively analyzed. All patients received DECT before surgery without any neoadjuvant therapy. The diagnostic value was assessed using the iodine concentration (IC). Results In the pathological findings, 35 (43.2%) LNs from 13 patients were metastatic and 46 (56.8%) LNs from 17 patients were non-metastatic. The mean IC of metastatic LNs in the portal venous phase (PP) was 1.60 mg/ml, which was significantly lower compared with non-metastatic LNs (3.25 mg/ml, p < 0.001). Receiver operating characteristic (ROC) analysis revealed that the IC in PP had the highest ability to discriminate LN metastasis (area under the ROC curve AUC 0.932). The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of IC in PP (cutoff 2.1 mg/ml) were 87.0%, 88.6%, 85.3%, 90.0%, and 87.9%, respectively. When clinically obvious metastatic LNs in conventional CT findings were excluded, 50 LNs remained (5 metastatic and 45 non-metastatic LNs). In this subgroup analysis, the IC in PP remained the most powerful predictor of metastatic LNs (cutoff: 2.1 mg/ml, AUC 0.933). Conclusions The evaluation of IC in DECT may improve the diagnostic capabilities of discriminating metastatic LNs. This method may be particularly useful when conventional CT findings lead to equivocal results.