Oxymatrine reduces inflammatory cytokines, such as TNF-α and IL-17A, in the spleen and serum of CIA rats in a dose-dependent manner, downregulates the mRNA and protein levels of ROR-γt related to Th17 cells, and upregulates the mRNA and protein levels of Foxp3 related to Treg cells, which significantly reduced the severity of disease in CIA rats and eliminated symptoms, such as claw swelling, arthritis score, and synovial hyperplasia. The gene discussed is IL17A; the disease is Arthritis.