Abstract: Developmental endothelial locus-1(Del-1) is an extracellular matrix(ECM) protein, which is secreted by endothelial cells during the process of embryonic development and also expressed by various kinds of tumor cells. The roles of Del-1 in embryonic development, angiogenesis, anti-inflammatory and tumor progression are widely studied. Del-1 is expected to be a novel target of the diagnosis and therapy of many diseases, especially in tumor. The authors reviewed the research progress of the role of Del-1 in cellular microenvironment particularly in tumor microenvironment and discussed the prospective of the further research of Del-1.