[Objective] To discuss the effects of arsenic stress on the activities of antioxidant enzymes in medicinal plant Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao, so as to provide a theoretical basis for revealing the arsenic toxicity mechanism on plants. [Method] Using Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao as tested materials, potassium permanganate titration, guaiacol method, pyrogallol autooxidation methods and thiobarbituric acid method were respectively adopted to study effects of arsenic stress on catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) activities and malondialdehyde (MDA) concentrations. [Results] With the increase in concentration of arsenic, the activities of CAT, PCD and SOD in Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.)Hsiao could be maintained, especially POD. From the view point of dynamic time, CAT activity increased firstly then declined, POD activity increased and SOD activity changed little along with the increasing treatment time. Besides, MDA content increased firstly and then decreased that reached the maximum on 8th day. [Conclusions] The study could provide theoretical basis for control of heavy metals in traditional Chinese medicine and identification of pharmacological activities. [Objective] To discuss the effects of arsenic stress on the activities of antioxidant enzymes in medicinal plant Astragalus membranaceus (Fisch.) Bge. Var. Mongholicus (Bge.) Hsiao, so as to provide a theoretical basis for revealing the arsenic toxicity mechanism on plants. [Method] Using Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao as tested materials, potassium permanganate titration, guaiacol method, pyrogallol autooxidation methods and thiobarbituric acid method were different to studied effects of arsenic stress on Results with the increase in concentration of arsenic, the activities of CAT, PCD and SOD in Astragalus membranaceus (Fisch.) Bge [Results] With the increase in concentration of arsenic, the activities of CAT, PCD and SOD in Astragalus membranaceus (Fisch.) Bge . var. mongholicus (Bge.) Hsiao could been maintained, especially POD. From the view point of dynamic time, CAT activity increased first then declined, POD activity increased and SOD activity change In addition, MDA content increased first and then decreased that reached the maximum on 8th day. [Conclusions] The study could provide theoretical basis for control of heavy metals in traditional Chinese medicine and identification of pharmacological activities.