Anti-angiogenesis therapy is an established therapeutic strategy for cancer. The endogenous angiogenic inhibitor angiostatin contains the first 3–4 kringle domains of plasminogen and inhibits both angiogenesis and vascular permeability. We present here a 10-residue peptide, Angio-3, derived from plasminogen kringle 3, which retains the functions of angiostatin in inhibiting both angiogenesis and vascular permeability. NMR studies indicate that Angio-3 holds a solution structure similar to the corresponding region of kringle 3. Mechanistically, Angio-3 inhibited both VEGF- and bFGF-induced angiogenesis by inhibiting EC proliferation and migration while inducing apoptosis. Inhibition of VEGF-induced vascular permeability results from its ability to impede VEGF-induced dissociation of adherens junction and tight junction proteins as well as the formation of actin stress fibers. When administered intravenously, Angio-3 inhibited subcutaneous breast cancer and melanoma growth by suppressing both tumor angiogenesis and intra-tumor vascular permeability. Hence, Angio-3 is a novel dual inhibitor of angiogenesis and vascular permeability. It is valuable as a lead peptide that can be further developed as therapeutics for diseases involving excessive angiogenesis and/or vascular permeability