Abstract: Objective To study the function of thioredoxin reductase 2(TrxR2)gene in a rsenic-resistance(As- ECV 304)cells.Methods The prote in level of TrxR2 in As-ECV 304 and control ECV 304 cells was detected by Wes tern Blot and the cell cycles were detected by flowcy tometry(FCM).Three short in terfering RNA(siRNA)of TrxR2 gene and negative controls iRNA were made from chemical synthesis.As-ECV 304 cells transfected with 3 TrxR2 siRNA and control siRNA were exposed to NaAsO₂ for 72 hours and the effect of RNA in terference was studied by Western Blot.As-ECV 304 Cells transfected secondly with the TrxR2 siRNA,control siRNA and un-transfected were cultured for 24 hours and then exposed to NaAsO₂ for 24 hours.Cell viability and a rsenic to lerance were analyzed by MTT assay.Results Western Blot showed that the TrxR2 prote in level was highe rin As-ECV 304 cells than in control ECV 304 Cells.Cell cycle of As- ECV 304 cell and control cell showed different percent in phase and the percent of G0/G1 phase was higher in As-ECV 304 cells.One of three TrxR2 siRNA can specially in terfered target gene expression.MTT assay showed that the cell viability was obviously decreased in cells transfected with TrxR2 siRNA than control siRNA.The 50%inh ib iting concentration (IC₅₀)of As-ECV 304 cells transfected with TrxR2 siRNA,control siRNA and without transfection exposed to NaAsO₂ was 9.13μmol/L,15.8μmol/L and 18.52μmol/L,respectively.Conclusion The arsenic to lerance of As-ECV 304 cells transfected with TrxR2 siRNA significantly decreased,the TrxR2 gene may play an importan trole in arsenic to lerance of As-ECV 304 cells.