Abstract: Objective 　To investigate the apoptosis in human osteosarcoma cells induced by paclitaxel, and the relationship between this apoptosis and expression of bcl-2 and bax. Methods 　MG63 OS cells were treated with various concent rations of paclitaxel. Proliferation was determined by cell count in a cytometer chamber. Viability was assessed by typan blue dye exclusion. The cell morphologic alterations were visualized using light and transmitting elect ron microscope. The percentage of apoptosis of osteosarcoma cell MG63 was measured by TdT-mediated dU TP Nick End Labeling technique ( TUNEL) staining method and flowcytometry using Annexin V/ PI double staining method af ter 0, 24, 48, 72 and 96 hours of culture in the presence or absence of paclitaxel. The expression of apoptosis-regulated gene bcl-2 and bax were detected using immunohistochemical staining. Results 　A time-dependent and dose-dependent cell growth inhibition was shown after exposure to paclitaxel. Paclitaxel induced MG63 cells to undergo apoptosis with typical apoptosis characteristics, including morphological changes of chromatin condensation, chromatin crescent formation, nucleus fragmentation. The DNA-cleavage was detected by using TUNEL assay. The cells t reated with paclitaxel showed initially G₂ / M phase arrest, which was followed by apoptosis. Paclitaxel could reduce the expression of apoptosis-regulated gene bcl-2 and improved the expression of apoptosis-regulated gene bax. Conclusion 　Paclitaxel is able to induce the apoptosis in human osteosarcoma cells through the initiation of G₂ / M phase arrest and inhibiting mitosis in both a time-dependent and dose-dependent manner. This apoptosis maybe mediated by down-expression of apoptosis-regulated gene bcl-2 and up-expression of apoptosis-regulated gene bax.