Although actinomycin D (AMD) is known to induce apoptotic cell death to various cell lines, the mechanism of apoptosis induced by AMD is still unclear. Understanding this mechanism may improve its therapeutic efficacy. The present study has been performed to elucidate expression of Bcl-2 and Caspase-3 proteins related to apoptosis in human leukemia K-562 cells. Five different assays were performed in this study; DNA fragmentation analysis by agarose gel electrophoresis, quantitative assay of fragmented DNA, morphological assessment of apoptotic cells, quantification of apoptosis by annexin V (AV) and propidium iodide (PI) staning, and expression of Bcl-2 and Caspase-3 proteins by the western blot analysis. The number of apoptotic cells and amount of fragmented DNA in this cell line treated with AMD was increased at 6 hour. DNA ladder pattern was also appeared at 6 hour. The expression of Bcl-2 was decreased, and disappeared from 12 hours after AMD treatment. Precursor of Caspase-3 was degraded, and 20 kDa cleavage products were detected. These results suggest that AMD induced apoptosis of K-562 cells is Caspase-3-dependent fashion, and this apoptosis is related to the degradation of Bcl-2 proteins.