Lymph node metastasis (LNM) is a key factor for selection of treatment method and patients' prognosis in oesophageal squamous cell carcinoma (ESCC). However, no biomarkers able to support the clinical detection of LNM have been reported. Recently, vascular endothelial growth factor C (VEGF-C) was found to be a more accurate marker of LNM in lung cancer than computed tomography. Midkine is a multifunctional cytokine involved in cancer development. We investigated circulating midkine levels in ESCC patients (n=73) compared with those in healthy subjects (n=42) with double-antibody-sandwich indirect enzyme-linked immunosorbent assay (DASI-ELISA). We found that midkine was elevated in ESCC and involved in metastatic disease. Serum midkine (sMK) was a good marker of LNM, evaluated both clinically and pathologically, as revealed by ROC analysis. It also correlated with serum levels of VEGF-C. The increase of sMK was related to cancer cells, although a weak correlation was observed between sMK and platelet and leucocyte counts.