OBJECTIVE To study the mitigation effect and its possible mechanism of Astragalus membranaceus polysaccharide on the pulmonary hypertension induced by monocrotaline in rats. METHODS One hundred SD male rats were randomly divided into normal control group ，monocrotaline group ，A. membranaceus polysaccharide low-dose and high-dose groups. In addition to the normal control group

rats in other groups were injected with monocrotaline by single intraperitoneal injection of 60 mg/kg. On days 2 to 28 after administration ，rats in the A. membranaceus polysaccharide low-dose and high-dose groups were intraperitoneally injected with A. membranaceus polysaccharide of 200 mg/kg and 400 mg/kg，respectively，once a day. There were 25 rats in each group，and 15 rats were taken for index detection. The mean pulmonary artery pressure （mPAP）and right heart hypertrophy index （RVHI）were detected ，and morphology changes of pulmonary artery and cardiomyocytes were monitored . mRNA and protein expression of IL- 17 in their lung tissues were detected. RESULTS Compared with normal control group ，mPAP and RVHI of monocrotaline group and A. membranaceus polysaccharide groups were increased significantly （P＜0.01）；mRNA and protein expression of IL- 17 in lung tissues were significantly increased （P＜0.01），and there were obvious pathological changes in pulmonary artery and cardiomyocytes. Compared with monocrotaline group ，mPAP and RVHI were significantly decreased in A. membranaceus polysaccharide groups （P＜0.01），while mRNA and protein expression of IL- 17 in lung tissue were decreased significantly （P＜0.01）；pathological changes in pulmonary artery and cardiomyocytes were improved. Compared with A. membranaceus polysaccharide low-dose group ，above indexes and pathological changes were improved significantly in high-dose group. CONCLUSIONS A. membranaceus polysaccharide can reduce monocrotaline-induced pulmonary hypertension ，improve pulmonary artery structure and myocardial remodeling in rats ， the mechanism of which is presumably related to the down-regulation of IL- 17 expression in lung tissue of rats.