There is a critical need for more effective therapeutic approaches for cancer. Vernonia amygdalina Delile (VAD) has been used in African traditional medicine for the prevention and/or treatment of several diseases including diarrhea, intestinal illnesses, and cancer. However, the effects of VAD on human lung cancer and human prostate cancer cells remain largely unknown. The aim of this study was to explore a novel cellular staining protocol using acridine orange/propidium iodide (AO/PI) and to test the antiproferative activity of VAD against human lung cancer (A-549) cells and human prostate cancer (PC-3) cells. Our studies demonstrate that VAD inhibits the proliferation of both A-549 and PC-3 cells in a dose-dependent manner. This finding suggests that VAD may be useful in lung and prostate cancer prevention. However, further research is needed to elucidate the chemopreventive effects of VAD against cancer