Abstract： Objective： To observe the effect of Taohong Siwu Decoction on the improvement of joint swelling in rat models with rheumatoid arthritis(RA) and discuss its mechanism. Methods：With a total of 75 female SPF Wistar rats， 60 rats were selected as rat models with RA， and the rest of 15 rats were included into the blank group. After successful modeling，a total of 60 rats were randomly divided into the model group and the Taohong Siwu Decoction groups of low-dose，medium-dose and high-dose(6.53 g/kg， 13.06 g/kg and 26.13 g/kg)，with 15 rats in each group. All groups were administrated for four weeks. The swelling of right limbs of rats in each group was evaluated by Arthritis Index(AI) scoring； the contents of matrix metalloproteinase- 8(MMP- 8) and tissue inhibitor of metalloproteinase- 3(TIMP- 3) were measured by enzyme- linked immunosorbent assay； the pathological changes of synovial tissue of joints of rats in each group were observed by hematoxylin- eosin staining； the protein contents of Toll- like receptor 4 (TLR4) and nuclear factor-κB(NF-κB) of the synovial tissue of joints of rats in each group were detected by Western blot. Results： After intervention， the scores of AI， MMP- 8 content， and protein contents of TLR4 and NF- κB in the model group were significantly increased when compared with those in the blank group(P＜0.05)， and the TIMP- 3 content was decreased(P＜0.05)； compared with those in the model group，the scores of AI，MMP-8 content and protein contents of TLR4 and NF-κB in the Taohong Siwu Decoction groups of low-dose，medium-dose and high-dose were decreased(P＜0.05)，and the TIMP-3 content was increased(P＜0.05). Compared with those in the blank group，the inflammatory cells infiltration and synovial cell proliferation were found in the synovial tissue of joints of rats in the model group；after intervention，the pathological changes of the synovial tissue of joints of rats in the Taohong Siwu Decoction groups of low- dose， medium- dose and high- dose were significantly improved. Conclusion： Taohong Siwu Decoction can effectively improve the symptom of joint swelling of rats and reduce the inflammatory responses，and its mechanism is related to the down regulation of protein expression of the TLR4/NF-κB signaling pathway，decrease of the MMP-8 content and increase of the TIMP-3 content.