Abstract: Objective To investigate the role of Th17 cells of synovial fluid （SF）in the pathogenesis of rheumatoid arthritis （RA）．Methods RA patients with knee synovial fluid （n=15）and healthy volunteers（n=15）were enrolled．The amounts of Th17 cells in peripheral blood and SF were measured by flow cytometry. Since there was no SF in healthy control, only the amounts of Th17 cells in peripheral blood were measured. The correlation between the amounts of SF Th17 cells and clinical inflammatory parameters was evaluated. Retinoic acid-related orphan receptor gammat (RORγt)， interleukin-17 (IL-17) gene expression in lymphocytes were assessed by real-time PCR．Results ① The percentages of Th17 cells in SF from RA patients （1.89±0.88）% were significantly higher than that in paired PB from RA patients （1.03±0.57）% and that in PB from healthy controls （0.35±0.18）%；②The frequency of Th17 cells in SF from RA patients correlated positively with serum CRP （r=0.519，P=0.047）；③ The mRNA levels of RORγt and IL-17 were increased in SF lymphocyte population from RA patients compared to paired PB from RA patients and healthy controls （P<0.01）．Conclusion Increases of Th17 cells in synovial fluid of patients with RA patients might attribute to the difference between local joint inflammation and systemic inflammation, and participates in joint damage．