Neovascularization is associated with the regulation of tissue development, wound healing, and tumor metastasis. A number of studies have focused on the role of heparin-like molecules in neovascularization; however, little is known about the role of heparin-degrading enzymes in neovascularization. We report here that the heparin-degrading enzymes, heparinases I and III, but not heparinase II, inhibited both neovascularization in vivo and proliferation of capillary endothelial cells mediated by basic fibroblast growth factor in vitro. We suggest that the role of heparinases in inhibition of neovascularization is through depletion of heparan sulfate receptors that are critical for growth factor-mediated endothelial cell proliferation and hence neovascularization. The differences in the effects of the three heparinases on neovascularization could be due to different substrate specificities for the enzymes, influencing the availability of specific heparin fragments that modulate heparin-binding cytokines involved in angiogenesis.