Abstract： Objective To determine the level of anticyclophilin A auto-antibodies (ACA) in sera of patients with psoriasis. Methods Cyclophilin A (CyPA) was extracted and purified from bovine thymus. The level of anticyclophilin A auto-antibodies (ACA) was detected by enzyme-linked immunosorbent assay (ELISA) and immunoblotting test (IBT) in sera of patients with psoriasis. Results It was shown that the level of ACA was significantly higher in the sera of patients with psoriasis than those in control group (IBT:P<0.01,ELISA:P< 0.01). ACA was found to be positive in 41.3％ of the patients by ELISA. In psoriatic group, the serum level of ACA was higher during the progressive stage than that in the stationary stage, however, no significant difference was observed (IBT:P>0.05,ELISA:P >0.05). Conclusion The results suggest that there is autoimmunological mechanism in the pathogenesis of psoriasis.