It has been proposed that flavonoids may have potential as anticancer agents. In this study, we showed that tartary buckwheat flavonoid (TBF) obviously inhibits the growth of human acute myelogenous leukemia (AML) HL-60 cells by MTT assay. The inhibitory effect of TBF on the proliferation of HL-60 cells is related to the induction of apoptosis, which is confirmed by DNA ladder formation on gel electrophoresis and apoptosis morphological changes under light microscope. Furthermore, HL-60 cells undergo rapid apoptosis upon treatment with TBF, as indicated by increased annexin V binding capacity and caspase 3 activation with flow cytometric analysis. Thus, our data provide a potential mechanism for the chemopreventive activity of tartary buckwheat flavonoid and suggest that it may have a potentially therapeutic role for human leukemia.