Background: Ulcerative colitis (UC) is a chronic inflammatory disease characterized by recurrent inflammation and ulcerations of colonic mucosa causing frequent episodes of bleeding per rectum.      The diagnosis of UC is best made with colonoscopy and mucosal biopsy for histopathology. Noninvasive tests, including C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), white blood cells (WBC), fecal calprotectin are being widely recognized , both for initial diagnosis and for accurately monitoring disease activity in UC. Objective: Evaluation of the level of serum adenosine deaminase in correlation to the activity of Ulcerative colitis. Patient and Methods: In this Prospective study evaluation the level of serum adenosine deaminase in correlation to the activity of UC was done in 80 patients. They were divided into 3 groups, Group I: 30 patients confirmed and well known cases of ulcerative colitis (by colonoscopy and histopathological examination), during remission state. Group II: 30 patients confirmed and well known cases of ulcerative colitis (by colonoscopy and histopathological examination), during exacerbation state (activity state). Group III: 20 patients with colonic manifestations other than ulcerative colitis. Results: The current study showed that ADA, the cut-off was 9.32 U/L to differentiate between exacerbation and remission states with sensitivity of 82.3%, specificity of 84.5%. Conclusion: Serum ADA is more accurate than CRP, WBCs and ESR to differentiate between exacerbation and remission states of UC.