CXCL4, also known as platelet factor 4 (PF-4), is one of the most plentiful platelet chemokines.Depending on the cell type, CSCL4 may has several biological functions. CXCL4 is mainly produced in megakaryocytes, released from the α-granules of platelets as a tetramer at micromolar concentrations depending on platelet activation. CXCL4 has both procoagulant and anticoagulant activities, thereby can bind heparin and neutralize the anticoagulant effect of heparin. In addition, CXCL4 also have functions such as inhibiting factor XII, and vitamin K dependent coagulation factor, and stimulating activated protein C generation. As a strong tumor inhibitor, CXCL4 can inhibit endothelial cell migration, proliferation, and in vivo angiogenesis through interfering with the angiogenic effect of growth factors such as FGF and VEGF.