Background: Ulcerative colitis (UC) is the commonest type of inflammatory bowel diseases (IBD) all over the world .Aim of the work: Compare the level of serum anti-outer membrane protein C (anti-Omp C) in UC patients and non-ulcerative colitis patients and correlate its level with the disease activity. Patients and methods:This study included 45 patients with UC and 45 non-ulcerative colitis patients. All cases were submitted to history taking, clinical examination and laboratory analysis (including assessment of antiompc antibodies). The cases in the UC group underwent colonic biopsy followed by microscopic histological examination of the obtained samples. Results: Endoscopic Activity Index for UC shows that 71.2% had active UC while 28.8% had inactive UC. The level of anti-ompc antibodies showed a statistically significant increase in the UC-group as compared with the non-UC group (31.11 ± 21.67 and 16.41 ± 15.06 respectively) (p < 0.001). The active UC group had statistically significantly higher level of anti-ompc antibodies as compared with the inactive cases (38.15 ± 18.02 and 26.61± 15.89 respectively) (p=0.005). ROC curve shows that,the best cut off point of anti-ompc level to identify cases with UC from non-ulcerative group was >13.8 with 63.4% sensitivity and 77.6% specificity (p < 0.001).Conclusion: Anti-OMPC may be a useful marker not only for diagnosis of UC but also in determination of the disease activity among UC patients.