Abstract: Objective To investigate the effects of naja naja atra venom( NNAV) on human erythroleukemia / adriamycin cells ( K562/ADM cells) and primary culture cells of early onset refractory acute myelogenous leukemia. Methods We studied 10 cases of the cells mentioned above. After having being treated with different concentrations of NNAV, cell proliferations were all oberved with the method of Thiazolyl Blue Tetrazolium Bromide( MTT ). Expressions of Bcl-2, the apoptosis-related proteins, was studied through the immunocytochemistry assay. Besides, flow cytometry was used to measure their apoptosis rate and effects of NNAV on cell cycle, and Western blot was for caspase-3 expression. Furthermore, we detected cyclin D expressions of the primary culture cells of early onset refractory acute myelogenous leukemia alone, and above methods were used to find difference in the cyclin-D-positive expression group and the negative group. Results After different concentrations of NNAV treated, both of the K562/ADM cells and primary culture cells of early onset refractory acute myelogenous leukemia resulted in a falled Bcl-2 and a raised caspase-3 expression, as well as cell proliferations obviously suppressed, and they were found to be time and dose-dependent. NNAV with concentration of 0.8μg/mL and 1.0μg/mL could made cell cycle of the primary culture cells of early onset refractory acute myelogenous leukemia arrest in the G0/G1 phase, while the cell contents decreased at the G2 / M phase. For the primary culture cells of early onset refractory acute myelogenous leukemia alone, we observed 7 of 10 were with CyclinD positive expression, the other 3 were with negative results. However, it was of no significant difference in the cyclin-D-positive expression group and the negative group. Conclusion This vitro study revealed that NNAV significantly inhibited cell proliferations of both K562/ADM cells and primary culture cells of early onset refractory acute myelogenous leukemia, and it also helped to regulate the cell cycle arrest in the G0/G1 phase, reduce the cell content in the G2 / M phase. Our experiment suggested that NNAV possibly inhibited the cell proliferations of primary culture cells of early onset refractory acute myelogenous leukemia through the intervention of Bcl-2 and caspase-3 expression and induced them apoptosis.