Although tremendous effort has been made over the past century to treat cancer effectively, the pace of drug development is far behind the increasing rate of cancer incidence and mortality. There are two major hurdles in anticancer drug development: dose-limiting toxic side effects that reduce either drug effectiveness or the quality of life of patients and complicated drug development processes that are costly and time consuming. Drug repositioning has recently gained increasing attention among cancer researchers as this approach utilizes existing drugs and is significantly cost- and time-effective. Existing drugs, particularly non-cancer drugs, have favorable safety profiles in humans and serve as an ever-increasing source for new anticancer drug discovery. Here we review the recent examples of drug repositioning of existing non-cancer drugs for preclinical and clinical introductions of cancer therapy.