The intestine is the largest mucosal organ of the body and also the first line immune homeostasis. Inflammatory bowel disease or IBD is divided into ulcerative colitis and Crohn's disease. One of the problems that can occur with UC is dietary allergy to some foods. This study aimed to evaluated the dairy allergy among patients with ulcerative colitis. This study is a Case - control study, that studied 72 patients with Ulcerative Colitis, after recording history of the disease, colonoscopy and confirmed by biopsy and 72 person without history of colitis. In this study, in order to investigate of food allergy, used of the EUROMMUM kit with an international code number DP3420-1601-11E. We used chi-square and Monte Carlo method for analysis of data. Among UC patients, 30.6% mild, 52.8% moderate and 16.6% of cases were in sever stage. 9.7% of them reported a history of abdominal surgery due to disease. According to the chi-square and Monte Carlo methods, dairy allergy (including: cow milk, cow milk UHT and casein) in UC group was significant (P=0.00). This study indicated that there is significant relationship between UC and cow milk, cow milk UHT and casein. UC patients who are allergic to dairy products and the use of dairy products can increase the severity of UC.