Objective: To observe the effects of Xinfeng Capsule (XFC), a compound Chinese herbal medicine, on behaviors and myocardial ultrastructure in adjuvant arthritis (AA) rats.Methods: Fifty-five rats were randomly divided into normal control group, untreated group, methotrexate (MTX) group, Tripterygium wilfordii glycosides tablet (TGT) group and XFC group. There were 11 rats in each group. Except for those in the normal control group, the rats in the other groups were all intracutaneously given 0.1 ml Freund's complete adjuvant in the right hind limb. Changes of behaviors and myocardial ultrastructure of the rats in different groups were observed.Results: Voix pedis' swelling and arthritis index in XFC, MTX and TPT groups were all obviously improved as compared with the untreated group. After XFC treatment, the autonomic activities were obviously increased, number of errors in exercise period and test period were obviously decreased, step-down latency (SDL) was lengthened and escape latency (EL) was shortened. Overall structure of myocardial myofibril and the majority of cristae was intact in XFC group. The effects of XFC in improving the behaviors and myocardial ultrastructure were better than those of MTX and TPT.Conclusion: Changes of behaviour and myocardial ultrastructure of AA rats can be observed. XFC can improve the myocardial ultrastructure of AA rats as well as their behaviors.