ObjectiveTo investigate the effects of Fangji Fulingtang on macrophage polarization and oxidative stress in the mouse model of myocardial fibrosis. MethodThe mouse model of myocardial fibrosis was established by subcutaneous injection of isoproterenol （ISO， 5 mg·kg^-1·d^-1）. Fifty C57BL/6J mice were randomly assigned into control （0.9% NaCl）， model （0.9% NaCl）， low- and high-dose （3.315 g·kg^-1·d^-1 and 13.26 g·kg^-1·d^-1， respectively） Fangji Fulingtang （FFD-L and FFD-H， respectively）， and metoprolol tartrate （Meto， 15 mg·kg^-1·d^-1） groups， with 10 mice each group. After 2 weeks of treatment， the heart appearance， cardiac weight index （CWI）， heart weight （HW）/tibia length （TL） ratio， and myocardial histopathological alterations were observed. Meanwhile， the serum levels of creatine kinase-MB （CK-MB）， transforming growth factor-β₁ （TGF-β₁）， tumor necrosis factor-α （TNF-α）， interleukin （IL）-1β， IL-6， IL-10， malondialdehyde （MDA）， superoxide dismutase （SOD）， and glutathione （GSH） were measured by enzyme-linked immunosorbent assay （ELISA）. The expression levels of CD86 and CD206 were observed by immunohistochemical staining. ResultCompared with the model group， the FFD-L， FFD-H， and Meto groups showed improved heart appearance， decreased CWI and HW/TL ratio （P<0.01）， lowered serum levels of CK-MB， TGF-β₁， TNF-α， IL-1β， and IL-6 （P<0.05， P<0.01）， and elevated IL-10 level （P<0.05）. Furthermore， the three groups showed reduced infiltration of inflammatory cells， myocardial injury， collagen deposition， and myocardial fibrosis， decreased CD86， SOD， and GSH （P<0.01）， and increased CD206 and MDA （P<0.01）. ConclusionFangji Fulingtang can mitigate ISO-induced myocardial fibrosis by regulating macrophage polarization and oxidative stress.