Objective To explore the effect of serum from Xinfeng Capsule(XFC)-treated rats on the proliferation and apoptosis of fibroblast-like synoviocytes in rheumatoid arthritis (RA-FLS) by regulating the circular RNA Cbl oncogene B (circ-CBLB). Methods XFC was administered orally to rats to prepare drug-containing serum. Human RA-FLS were stimulated with 100 μL of 10 ng/mL tumor necrosis factor-alpha (TNF-α) to establish the model. pcDNA3.1-circ-CBLB and negative control were constructed and transfected into RA-FLS. The experiment was divided into six groups: control group, TNF-α treated RA-FLS group, XFC treated RA-FLS group, pcDNA3.1-circ-CBLB-NC, pcDNA3.1-circ-CBLB(overexpression group), pcDNA3.1-cicr-CBLB combined with XFC treated group(overexpression+XFC group). Cell viability was assessed by CCK-8 assay; cell cycle and apoptosis by flow cytometry, and the expression levels of circ-CBLB in each group by real-time quantitative PCR. The levels of inflammatory cytokines interleukin 4 (IL-4), IL-10, IL-6 and TNF-α were measured by ELISA. Results The optimal serum was 200 mL/L, and the treatment time was 72 hours; Compared with the model group at the same time point, the cell viability of XFC group, overexpression group, and overexpression+XFC group were lower, while the expression level and apoptosis rate of circ-CBLB were higher. The proportion of cells in S phase and G2 phase was higher. Additionally, the levels of IL-4 and IL-10 were higher, while the levels of IL-6 and TNF-α were lower. Conclusion XFC treatment upregulates the expression of circ-CBLB in RA-FLS, increases anti-inflammatory cytokines, decreases pro-inflammatory cytokines, inhibits the viability of RA-FLS, increases apoptosis rate, extends the cell cycle, suppresses the proliferation of RA-FLS, and promotes its apoptosis.