Objective：To study the expression of C -X-C motif chemokine receptor 4(CXCR4)on regulatory T cells(Tregs)in peripheral blood(PB)and synovial fluid(SF)of rheumatoid arthritis(RA)and its correlation with clinical characteristics；so as to explore the pathogenesis of RA involving CXCR4 ⁺ Tregs. Methods：①The PB samples of 51 RA patients and 40 healthy volunteers were collected，and the knee SF samples of 10 patients with RA and 8 patients with osteoarthritis(OA)were collected by puncture of joint cavity. Then the ratio of CD4⁺ CD25⁺ CD127- Tregs and CXCR4⁺ Tregs in PB and SF was detected by flow cytometry. Clinical data of RA were collected，and the correlation analysis was made with Tregs and CXCR4 ⁺ Tregs ratio in PB. ②The peripheral blood mononuclear cells(PBMC)of RA and healthy volunteers were separated by Ficoll density gradient centrifugation method. CD4⁺ T cells were sorted by immunomagnetic positive selection kit and placed in the upper chamber of Transwell. C-X-C motif chemokine ligand 12(CXCL12)was added to the lower chamber. After 24 hours，the cells of the lower chamber were collected，and the CD4 ⁺ CD25 ⁺ CD127^- Tregs migrated to the lower chamber were detected by flow cytometry. Results：①Compared with healthy controls，the ratios of Tregs and CXCR4⁺ Tregs in PB of RA decreased，and the ratios in the high disease activity group and the middle disease activity group were lower than those in the remission group(P ＜ 0.05). The ratio of CXCR4 ⁺ Tregs in PB of RA was negatively correlated with the level of erythrocyte sedimentation rate(ESR)，C-reactive protein(CRP)，interleukin-6(IL-6)levels and DAS28 score. ②The ratios of Tregs and CXCR4⁺ Tregs in SF of RA were significantly higher than those in SF of OA. ③The ratios of Tregs and CXCR4⁺ Tregs in SF of RA were higher than those in PB. ④Compared with healthy controls，the mobility of Tregs in PB of RA increased significantly. Conclusion：The ratios of Tregs and CXCR4 ⁺ Tregs in PB of RA decreased，which are related to disease activity. Tregs and CXCR4 ⁺ Tregs in SF of joint inflammation are higher than those in PB and SF of OA. Tregs increased in SF of RA may be migrated from PB through CXCR4.