Objective To study the mechanism of arsenic on human lung adenocarcinoma cells.Methods MTT,FCM and RT-PCR tests were used to investigate apoptosis levels induced by arsenic trioxide and the effect on LRP mRNA expression.Results 1.0μmol/L and 3.0μmol/L arsenic trioxide can decrease LRP mRNA expression.Conclusion Low concentration As_2O_3 may improve apoptosis of lung caner by decreasing LRP mRNA expression.As_2O_3 may be used to treat lung cancer but the results are not better than cisplatin.