［Abstract］Objective： To investigate the effects of Xinfeng Capsule (XFC) on pulmonary function and related mechanism in adjuvant-induced arthritis (AA) rats. Methods： The rats were randomly divided into five groups：normal control (NC),model control (MC) groups，methotrexate (MTX)，tripterygium glycosides tablet (TPT) and Xinfeng capsule (XFC) treatment groups.The adjuvant-induced arthritis model was established by intracutaneous injection of 0.1 mL Freund′s complete adjuvant in the right paw of rats; the drugs were given 19 d after model establishment.The toe swelling degree (E)，arthritis index (AI)，pulmonary function，peripheral blood Treg levels，pathological changes of lung tissue and expression of Foxp3，TGF-β1，Smad3，Smad7 proteins in lung tissue were measured 30 d after drug administration. Results： Compared to NC group，the levels of E，AI，alveolitis score，TGF-β1 and Smad3 were significantly increased (P<0.05 or P<0.01);maximum expiratory flow 25% of vital capacity (FEF25)，50% maximal expiratory vital capacity flow (FEF50)，maximum expiratory flow at 75% of vital capacity (FEF75)，maximum mid-expiratory flow (MMF)，force peak expiratory flow (PEF)，CD4+ CD25+ Treg，Foxp3 and Smad7 were significantly decreased in MC group (P<0.05 or P<0.01）.Compared to MC group，the expression of E，AI，TGF-β1 and Smad3 were reduced，while FEF50，FEF75，MMF，PEF，Treg，Foxp3 and Smad7 were elevated in XFC group (P<0.05 or P<0.01）.Compared to XFC group,the level of body mass，FEF25，FEF50，FEF75，MMF and Treg were lower in MTX and TPT groups (P<0.05 or P<0.01）. Conclusions： There are inflamed joints and reduced pulmonary function in rats of adjuvant-induced arthritis.XFC can inhibit paw edema degrees，reduce arthritis response，and improve pulmonary function，which is associated with up-regulating expression of Treg and Foxp3， down-regulating the expression of TGF-β1 and adjusting TGF-β1/Smads signal pathway.