Objective : To investigate whether arsenic trioxide (AS_2iO_3)-mediated apoptosis of synovial cells has potential as a new therapeutic drug in rheumatoid arthritis(RA) through culture the synoviocytes and the control in vitro.Methods: primary synovial cells were cultured by means of two-enzymatic digestion, we adopt the cell from thirth to twelfth in this test. The cultured cells were defined by light microscope , flow cytometry(FCM),MTT. Apoptosis changes were examined in synovial cells of 5 RA , 3 normal controls (NC,cases of trauma)by FCM and colorimetric assay at 48h . Results:1. Certain concentration of AS_2O_3 could inhibit the viability of synoviocytes at 48h, which was dose-dependent by means of MTT .2. Certain concentration of AS_2O_3 could induce the apoptosis of synoviocytes pro rata at 48h, which was dose-dependent by means of FCM.3. By means of colorimetric assay we fond the activity of caspase 3 could be increased in synovial cells lysates on certain concentration of AS_2O_3 at 48h.Conclusion: Certain concentration of AS_2O_3 could induce the apoptosis of synoviocytes and caspase 3 play a role in apoptosis , which provide useful help for choosing clinically adequate therapeutic drugs and doses for RA.