Abstract Background & Objectives: Ulcerative colitis (UC) affects the mucosa of the rectum and the colon, and is characterized by flares and remission. It is observed that defect of proliferation of T-lymphocytes is the causative factor of ulcerative colitis. Vitamin D appears to play an important role in decreasing the incidence of active UC. The study was undertaken to determine the effect of Vit.D in patients with ulcerative colitis (UC). Place & Duration of Study: This study was conducted from January 2014 to January 2016 in Mayo Hospital, Lahore, Pakistan. Methodology: Data was collected from patients suffering from UC who visited the surgical out-patient department and/or were admitted to the surgical floor. A total of 84 patients within the age range of 18-70 years and divided into two equal groups of 42 were included in the study. The control group was given standardized treatment of ulcerative colitis according to severity of disease as measured by Truelove and Witt's criteria. The intervention group was given an additional dose of Vitamin D along with primary disease treatment. Results: It was seen that patients in the intervention group showed significant remission and a decrease in the frequency of relapses. Conclusion: Our study supports the hypothesis that vitamin D supplementation helps to achieve significant remission and reduce relapse in patients suffering with active ulcerative colitis.