Several approaches have been developed to improve the ability of anticancer drug to more specifically target tumors and avoid normal organs. One of the most effective strategies is to encapsulate drugs in particles that deliver them preferentially to tumor sites. For example, liposome particles have been found able to deliver radionuclides, genes, and chemotherapeutic agents to tumor sites. [6] [7] [8] [9] [10] . Another promising strategy is to encapsulate anticancer drugs in liposomes conjugated with moieties, such as antibodies and peptides, that target particular types of target tumor cells or tumor vasculatures [11] [12] [13] . Use of internalizing ligands for targeting liposomes conjugated with such moieties makes it possible to deliver the chemotherapeutic drugs encapsulated within them to the cytosol through the receptor-mediated endocytosis [14] [15] [16] [17] . This article reviews the current research in developing liposomal drug delivery systems that use peptide ligands to target blood vessels in solid tumors. We discuss the identification of peptides that can target tumor blood vessels and the use of targeting and nontargeting 12 GGT GGA GGT TCG-3 Figure 1 : Selection of peptides that target tumor blood vessels using in vivo phage display. Peptide or antibody libraries are expressed as fusion proteins with a coat protein (pIII) of a bacteriophage, and the fused proteins are displayed on the surface of the virion. A phagedisplayed peptide library was injected through the tail vein of tumor-bearing mice. Eight minutes after injection, the mice were perfused through the heart. Phage recovered from the tumor was amplified and reinjected in mice for another four rounds. Tumor-targeting phages were further identified by in vivo tumor-homing assay, synthetic peptide binding and competition assay, and immunohistochemical staining. The identified peptides can be used as ligands to recognize cell surface markers or tumor antigens to develop targeted therapy. SCID mice bearing human cancer xenografts were successfully treated with ligand-conjugated antiangiogenic targeting liposomes.