Abstract: OBJECTIVE To study the effects of puerarin on pulmonary vascular remodeling in rats with pulmonary hypertension induced by chronic hypoxia and hypercapnia .METHODS Thirty Sp rague-Dawley rats were randomly divided into normal control group (NC) , hypoxic hypercapnia group (HH) and hypoxic hypercapnia + puerarin group (HP). Mean pulmonary arterial pressure (mPAP) and mean carotid arterial pressure (mCAP) were measured. MMP-2,MMP-9 and their mRNA were observed in pulmonary arterioles by the technique of immunohistochemistry and in situ hybridization. RESULTS (1)mPAP was significantly higher in rats of HH group than that of NC group and it was much lower in rats of HP group than that of HH group(P<0.01).Differences of mCAP were not significant in three groups.(2)Light microscopy showed media thickness of pulmonary arterioles was much higher in HH group than that of NC group,and vessel cavity turned more straiter in HH group than that of NC group.Howerer, the damage of pulmpnary arterioles in HP group was much slighter than that of HH group. (3) The levels of lung homogenates Hyr,MMP-2 and MMP-9 were much higher in rats of HH group than those of NC group(P<0.01),and lower in HP group than HH group (P<0.01).Plasma NO content of group HH was lower than that of group NC（P<0.01），it was highter in group HP than that of group HH（P<0.01）.(4)Expression of MMP-2,MMP-9 and their mRNA in pulmonary arterioles were significantly higher in rats of HH groups than those of NC group (P<0.01)，and they were lower in rats of HP group than those of HH group (P<0.01).CONCLUSION Puerarin can improve pulmonary vessel remodeling by regulate MMPs system in hypoxic hypercapnic rats.