Background Homoharringtonine (HHT) is a cephalotaxine ester derived from an evergreen tree found wildely throughout southern China, which has antileukemic activities against a variety of acute myeloid leukemic cells. For the sake of illustrating the mechanisms of HHT in the treatment of leukemia, we assessed the effect of HHT on the apoptosis of human chronic myeloid leukemic cell line K562.Methods The apoptosis of K562 cells induced by HHT was analyzed by transmission electron microscopy, agarose gel electrophoresis of DNA, flow cytometry and terminal deoxyribonucleotidyl transferase-mediated dUTP-biotin nick labeling.Results Characteristic apoptosis-related features emerged in K562 cells after exposed to HHT at a concentration 0.05-100 μg/ml. Transmission electron microscopy of HHT treated K562 cells displayed chromatin condensation and aggregation under the nuclear membrane, nuclear fragmentation and apoptosis body formation. Typical DNA ladder in agarose gel electrophoresis was observed in the cells exposed to HHT. The cell cycle analysis measured by flow cytometry showed G1 phase cells decreased with the increase of S phase cells while apoptosis was induced by HHT in K562 cells. The percentage of apoptotic cells in K562 cells treated with 50 μg/ml of HHT decreased significantly when pretreated with 1 μg/ml of cycloheximide, 0.05 μg/ml of Actinomycin D respectively.Conclusions HHT has apoptotic effects on K562 cells. The HHT induced apoptosis mainly of the cells in G1 phase and this process required RNA transcription and protein synthesis.