Abstract: Objective:To investigate the effect of BAX on the apoptosis of human laryngeal squamous cell carcinoma Hep 2 cells and their sensitivity to5-aza-2' deoxycitydine ( 5-Aza-CdR).Methods:The proliferation of Hep2 cells was detect-ed by methyl thiazolyl tetrazolium (MTT) colorimetry after treatment with 5-Aza CdR in vitro. The plasmid containing BAX cDNA was transfected into Hep2 cells. The mRNA level of BAX gene was detected by RT-PCR. Flow cytometry was used to analyze the apoptosis and cell cycle of Hep2 cells. Results: After treatment with different concentrations of 5-Aza-CdR, the proliferation of Hep 2 cells was inhibited by 5-Aza-CdR in vitro in a dose- and time-dependent manner, and the IC 50 was 4 μ mol /L. The resul ts of flow cytometry detection showed that both BAX and 5-Aza-CdR could block Hep 2 cells in G1/S phase and promote apoptosis. The percentage of cells in G0/G1 and the apoptotic rate of Hep 2 cells treated with 5-Aza-CdR were increased from51.57% to71.17% and from1.67% to13.96%, respectively. The RT-PCR results showed that transfec-tion of BAX significantly increased the expression of BAX gene level in Hep 2 cells ( P<0.05). After transfection, the percent-age of Hep 2 cells in S phase were decreased from 33.29% and 32.42% to16.07% and 13.58% in blank control group and empty vector transfected group, respectively. The apoptotic rate of Hep 2 cells transfected with plasmid containing BAX cD -NA was increased from7.13% to23.74%, with a significant difference from that of the blank control group and empty vector transfected group ( P<0.05). Conclusion:Transfection of BAX can induce apoptosis of Hep 2 cells and increase their sensitivi-ty to the killing effect of 5-Aza-CdR.