Modified anti-angiogenic peptides are disclosed. The modified peptides are capable of forming a peptidase stabilized anti-angiogenic peptide. The modified anti-angiogenic peptides, particularly modified kringle 5 peptides are capable of forming a conjugate with a blood protein. Conjugates are prepared from anti-angiogenic peptides, particularly kringle 5 peptides, by combining the peptide with a reactive functional group with a blood protein. The conjugates may be formed in vivo or ex vivo. The conjugates are administered to patients to provide an anti-angiogenic effect.