Objective To study immunologic mechanism of tigers urine on patients of rheumatoid arthritis. Method We used ELISA method to detect TNF values of serum; we also used MTT colorimetric method to detect the inhibition of tigers urine on T－ cell. Result TNF values of RA patients serums at both active stage and stationary phase before the therapy were higher than those of healthy group; TNF values of patients serums after the therapy were lower than those before the therapy; tigers urine had obvious inhibitive action on proliferation of peripheral bloods T－ cell. Conclusion Tigers urine could inhibit T－ cells proliferation and TNFs secretion, which may be the important mechanism of curing RA.