Background: Intestinal ultrasound [IUS] has been reported to be accurate in the diagnosis of Ulcerative colitis and can also be applied to determine the extent, severity and location of inflammation. The aim of this study was to evaluate the usefulness of bowel US in comparison to colonoscopy for assessing disease extent and activity of Ulcerative Colitis. Methods: This was a cross sectional study which included 60 patients with ulcerative colitis who attended Gastroenterology outpatient clinics and IBD unit of National Herpetology and Tropical Medicine Research Institute. Participants were divided into 2 groups of patients according to Truelove and Witt's criteria for classification of severity of ulcerative colitis. Group I (n= 30) active ulcerative colitis patients. Group II (n= 30) inactive ulcerative colitis patients (in remission). Results: In the present study, there were highly statistical significant difference between the studied groups regarding bowel wall thickness, Doppler signal, wall layer stratification and disease extent and in active group. Conclusion: IUS may represent a useful first-line, non-invasive tool for assessing activity, severity and extent of Ulcerative colitis.