Objective:To investigate the effects of survivin inhibitor YM155{1-(2-methoxyethyl)-2-methyl-4,9-dioxo-3-(pyrazin-2-ylmethyl)-4,9-dihydro-1H-naphtho[2,3-d] imidazolium bromide} on cell viability,apoptosis and Cysteinyl aspartate specific proteinase-3,Cysteinyl aspartate specific proteinase-8,Cysteinyl aspartate specific proteinase-9 of the thyroid carcinoma cell line B-CPAP in order to discuss mitochondrial mechanisms of apoptosis.Methods: B-CPAP cells were cultured in vitro and treated with YM155 at various concentrations(0,0.5,1,2,4,8 nmol/L)for 24,48 and 72h.The cell viability of B-CPAP cells were measured by CCK-8 assay.B-CPAP cells were randomly divided into 4 groups:B-CPAP cells were treated with YM155 at various concentrations(0,1,2 nmol/L)and 5 μmol/L Cisplatin(the positive control group)for 24 h.The effects of YM155 on B-CPAP cells apoptosis were evaluated by TUNEL and flow cytometry Annexin V-FITC/PI method.The expression level of Survivin and Caspase-3,Caspase-8 ,Caspase-9 were detected by Western blot analysis.Results: Compared with the 0 nmol/L group,YM155 significantly inhibited the cell viability of B-CPAP cells and induced their apoptosis (P<0.05 or P<0.01).Compared with the 0 nmol/L group,YM155 significantly reduced the expression level of Survivin and upregulated Caspase-3,Caspase-8 ,Caspase-9(P<0.05 or P<0.01).Conclusion: YM155 can inhibit the cell viability of B-CPAP cells and induce apoptosis,its possible mechanisms maybe related to upregulated expression level of Caspase-3,Caspase-8 and Caspase-9.