Beta-aescin, a natural triterpenoid saponin isolated from the seed of Chinese horse chestnut (Aesculus chinensis), is known to generate a wide variety of biochemical and pharmacological effects. In the present study, the authors investigated the anti-proliferative and apoptotic effects of beta-aescin in human chronic myeloid leukemia K562 cell line in vitro. The anti-proliferative effects were detected by CFU-K562 colony formation and cell viability assay. The apoptotic effects were analysed by morphological analysis, annexin V assay, DNA fragmentation assay and flow cytometry DNA content analysis. The results showed that beta-aescin exhibited potent dose- and time-dependent anti-proliferative effects in K562 cells. Morphological evidence of apoptosis, a significant increase of annexin V+ and PI- cells (early apoptotic) and apoptotic DNA fragmentation, were observed in cells treated with beta-aescin. Flow cytometry analysis revealed that beta-aescin could lead to an accumulation of sub G1 population in K562 cells, and suggesting a potential G1 phase accumulation in cell cycle profile of K562 cells. Our findings revealed that beta-aescin is a potent natural inhibitor of proliferation and inducer of apoptosis in K562 cells, and beta-aescin may be a candidate lead compound to explore potential antileukemia drugs.