Pm-VEGF, a novel member ofVEGF family from the venom gland of Taiwan habu (Protobothrops mucrosquamatu), is a disulfide-linked homodimer with 119 amino acid residues. Recombinant fusion Pm-VEGF was expressed in Escherichia coli, purified and refolded. Surface plasmon resonance was used to determine its binding kinetics toVEGF-receptors (VEGFR). Relative to human VEGF165, the binding affinity of Pm-VEGF to the VEGFR-1 was 1.7-fold higher while affinity to the VEGFR-2 was 17-fold lower. But it did not bind the VEGFR-3 or neuropilin-1. Pm-VEGF promoted the proliferation and tissue factor production of endothelial cells, the neovascularization in the chicken chorioallantoic membrane, and increased vascular permeability. It also stimulated tissue-factor production and human monocyte chemotaxis, in accord with its specificity for VEGFR-1. Structural comparison among VEGF-proteins from various viper venoms revealed that the two subfamilies of vipers (Crotalinae and Viperinae) have evolved with distinct receptor-specificities for VEGFR-1 and VEGFR-2, respectively. Discussion on structure-activity relationships of the VEGFs further provided insight into residues important for the receptor-binding and specificities.