Abstract Background Ulcerative colitis [UC] is a chronic inflammatory bowel disease characterized by relapsing and remitting episodes of inflammation usually limited to the mucosal layer of the colon. Treatment targets for UC patients nowadays include patient-reported as well as endoscopic remission. Recently, endoscopy is increasingly being used to guide treatment, because evidence suggests that mucosal healing is associated with improved long-term outcomes. However, it is challenging to repeatedly perform colonoscopies to assess mucosal disease activity due to the high cost and burden for the patient. Hence, alternative and reliable non-invasive methods to assess disease activity are needed. Aim of the Work The aim of this study is to to comparison colonoscopy versus bowel ultrasound in assessment of disease activity and severity in patients with Ulcerative Colitis. Patients and Methods This was a case control study, was conducted at Internal Medicine and Gastroenterology outpatient clinics in Ain Shams University over 90 patients suffering from morbid obesity and in whom surgical management is indicated. Participants were divided into two groups: Group (1): (n = 30) healthy individuals, matched for age and gender, group (2): (n = 60) Active and inactive (in remission) ulcerative colitis patients. Results The main findings of the study revealed that: There was no statistically significant difference between the studied groups as regard Demographic data. The mean age at diagnosis was 36.11 (±10.42 SD) with range (20-53), the mean duration of disease was 1.95 (±0.83 SD) and according to Disease extent there were 48 (80%) left-sided, 11 (18.3%) extensive and 1 (1.7%) pancolitis. There was high statistically significant difference between the studied groups as regard Laboratory investigations. There was high statistically significant difference between the studied groups as regard Radiological Examination. According to Endoscopic Findings there were 21 (35%) 0 or 1 (remission) and 39 (65%) 2 or 3 (active). There was high statistically significant relation between Endoscopic Findings and Laboratory investigations. There was high statistically significant relation between Endoscopic Findings and Radiological Examination. Conclusion BUS may represent a useful first-line, non-invasive tool for assessing endoscopic activity, severity, and extent, and may be helpful to determine in a rapid manner whether a significant flare has occurred and to guide the management of UC patients, delaying or avoiding colonoscopy when it is not needed. In addition, BUS may be preferred in clinical practice for monitoring disease course and for assessing short-term treatment response, reducing the necessity of repeated CS, although specific data on monitoring will be needed.