We recently reported that neovascularization of the vasa vasorum network occurs in the pulmonary artery (PA) adventitia of chronically hypoxic calves. Because extracellular adenine nucleotides are important regulators of vascular functions, we hypothesized that extracellular ATP may have a direct angiogenic effect on vasa vasorum endothelial cells (VVEC). We found that ATP dramatically increases DNA synthesis, migration, and tube formation on Matrigel in isolated VVEC. The PI3K/mTOR and ERK1/2 play a critical role in ATP‐induced mitogenic and migratory responses. However, only ERK1/2 contribute in part, to ATP‐induced tube formation on Matrigel. In contrast to VVEC, mitogenic responses to extracellular ATP were not observed in aortic and PA endothelial cells, indicating that VVEC, isolated from the sites of angiogenesis, exhibit a unique pro‐angiogenic phenotype with an augmented sensitivity to extracellular ATP. Further, using an in vivo Matrigel plug assay, we found subcutaneous injection of Matrigel containing MeSATP, ATPγ, MeSADP, and ADPβS resulted in plug neovessel formation (n=3). However, adenine nucleotides diminished the effect of total platelet lysates (n=11) on plug neovascularization (n=3). Together, our studies demonstrated that a fundamental molecule, ATP could be recognized as a potent regulator and/or modulator of angiogenesis in microvascular endothelial cells.(Supported by NIH grant: HL‐14985 and AHA grant: 0665464Z)