Objective To research the mechanism of Fengshining Capsule（FSN） for rheumatoid arthritis（RA）.Methods Sixty SD rats were randomized into the normal control group

model group

Tripterygium glycosides tablet（TGT） group

low-dose FSN group

middle-dose FSN group and high-dose FSN group

with 10 in each.The rat models with collagen-induced arthritis（CIA） were established in the five groups except the normal control group.The TGT group was given 0.03 g/（kg·d） TGT.The low-dose

middle-dose and high-dose FSN groups were given 0.33 g/（kg·d）

0.66 g/（kg·d） and 1.32 g/（kg·d） FSN capsule respectively.The distilled water was given to the normal control group and model group.Each group was intragastrically administrated with 20ml/kg of corresponding medicine

once daily for 4 weeks.The ultrastructure of synovial cells was observed with transmission electron microscopy and the expressions of caspase-3 and caspase-9 mRNA were detected with reverse transcription-polymerase chain reaction（RT-PCR） method.Results Comparing with the model group

the ultrastructure of synovial cells was improved in the FSN groups

especially in the middle-dose FSN group.Comparing with the model group

the expression of caspase-3 mRNA was significantly increased in the TGT group

low-dose FSN group and middle-dose FSN group（P<0.05 or P<0.01）.Comparing with the model group

the expression of caspase-9 mRNA was significantly increased in the TGT group

high-dose FSN group and middle-dose FSN group（P<0.05 or P<0.01）.Conclusion The mechanism of FSN capsule for RA may be relevant to improving the ultrastructure of synovial cells and increasing the apoptosis-related genes caspase-3 mRNA and caspase-9 mRNA.