Plants consumed by non-human primates represent potential drug sources for human disease management. In this study, we isolated kaempferol-3-O-rhamnoside as an active compound from the leaves of Schima wallichii Korth., a plant commonly consumed by non-human primates. Its anti-cancer activities, including its ability to induce apoptotic mechanisms, were investigated in MCF-7 breast cancer cells. Results showed that in MCF-7 cells, kaempferol-3-O-rhamnoside inhibits cell proliferation in a dose-dependent manner and promotes apoptosis via the activation of the caspase signaling cascade, which includes caspase-9, caspase-3 and PARP. Our results provide a basis for further exploration of kaempferol-3-O-rhamnoside as an active compound for potential anti-cancer therapeutics.