High-mobility group box 1 (HMGB1), a proinflammatory cytokine, plays an important role in inflammatory diseases, including severe sepsis and arthritis. This recent discovery of the extracellular role of HMGB1 as a multifunctional cytokine involved in tumorigenesis, tumor angiogenesis as well as metastasis has opened up a new field of research to study the role of HMGB1 in tumors. However, its molecular mechanism in lymphangiogenesis remains poorly understood. In this study, human lymphatic endothelial cells (LECs) were treated with human recombinant HMGB1 (rHMGB1) and recombinant VEGF-C (rVEGF-C). Changes in cell proliferation, migration, and the capillary-like tube formation were assessed by MTT assay, transwell chamber assay, and a Matrigel model, respectively. Human rHMGB1 induced LEC proliferation, migration, and tube formation in a dose- and time-dependent manner with the maximal effect at a concentration of 2 μg/ml. As a specific lymphangiogenes factor, the role of rVEGF-C in promoting lymphangiogenesis was significant. These data indicate, for the first time, that HMGB1 might contribute to tumor lymphangiogenesis and lymphatic metastasis, and it might ultimately represent a therapeutic target in tumor patients.