One of the most ubiquitous biomarkers of cancer is phosphatidylserine. It is expressed exclusively on the inner membrane leaflet of healthy vasculature, but tumor endothelium externalizes phosphatidylserine, taking advantage of its immunosuppressive signaling role. Annexin V is a small membrane binding protein that selectively binds to externally expressed phosphatidylserine and induces endocytosis. An annexin V-drug conjugate has been synthesized and characterized that is designed to deliver the cytotoxic drug payload to tumor cells. The cytotoxic activity was investigated in vitro using three breast cancer and two leukemia cell lines. This thesis describes the synthesis and characterization and reports the results of the in vitro experiments.