Abstract: Objective:To study the relationship between cyclophilin A (CyP A),its autoantibody and the activity of ulcerative colitis (UC).Methods:The CyP A levels of plasma and lymphocytes were detected by double sandwich ELISA in 67 active,49 inactive UC patients and 50 normal controls.Anti-CyP A autoantibody was measured by indirect ELISA.Results:The CyP A levels of plasma and lymphocytes in active UC subjects were significantly higher than those in inactive UC or normal controls (P<0.01).But there was no statistical significance between inactive UC and normal controls (P>0.05).The positive rate of anti-CyP A autoantibody in active UC patients was markedly higher than those in inactive UC or normal controls (P<0.01).Conclusions:The increase of CyP A levels of plasma and lymphocytes and the positive expression of anti-CyP A autoantibody in active UC patients are two useful markers which reflect the activity of UC.