It is known that the renin-angiotensin system (RAS) plays a fundamental role not only as a vasoconstrictor in controlling blood pressure and electrolyte/fluid homeostasis, but also as a mitogenic factor through the Ang-II type-1 (AT1) receptor in smooth muscle cells and cardiac myocytes. Angiotensin II (Ang-II) is indeed thought to be a growth factor, and Ang-II receptor blockers (ARBs), a class of antihypertensive agent, suppress signal transduction pathways mediated by several growth factors or cytokines, through the AT1 receptor. There is increasing evidence that the RAS is implicated in the development of various cancers. We previously demonstrated that ARBs have the potential to inhibit the growth of prostate cancer cells and tumors through the AT1 receptor. This review highlights the possibility of ARBs as novel agents for prostate cancer as well as other cancers, and reviews the literature on this area.