Objective To investigate the effects of trichostatin A (TSA) on Th1 and Th17 cells in the mice model of collagen induced arthritis (CIA).Methods Mice model of rheumatoid arthritis (RA) was induced in DBA/1 mice with type Ⅱ collagen.Paws were scored for histological severity of arthritis.The severity of inflammation of mice joints was evaluated by histological examination.Real time polymerase chain reaction (PCR) was used to determine mRNA of cytokines and transcriptional factors.Serum cytokine production was measured by enzyme linked immunosorbent assay (ELISA).T cell proliferation was examined by MTT method.One-way ANOVA and Student-Newman-Keuls were conducted in this study.Results The expressions of IFN-γand IL-17 mRNA of the CIA group were higher than that of the control group (8.27±0.64 vs 2.97±0.25,5.80±0.23 vs 0.70±0.26,all P＜0.01),but were inhibited significantly by TSA introduced at the onset of arthritis(6.60±0.52,2.50±0.41,all P＜0.01).Collagen specific T cell proliferation was significantly suppressed by the introduction of TSA.Increased level of IL-4 was observed in TSA treated group compared to that of CIA group(2.10±0.17 vs 1.01±0.08,P＜0.01).Conclusion Th1 and Th17 cells play crucial roles in the lesions of RA.TSA can suppress the progress of CIA by decreasing the percentage of Th1 and Th17.