Inflammatory bowel diseases are represented by two idiopathic disorders, which include ulcerative colitis and Crohn's disease. Ulcerative colitis is restricted to the colon and involves uncertain and inflammation of the lining (mucosa) of the large intestine. Crohn's disease, on the other hand, can involve the mucosa of the small and/or large intestine and may involve deeper layers of the bowel wall. The present invention contains N-acetylcysteine disposed in a pharmaceutically acceptable carrier for oral or rectal delivery for treating such inflammatory bowel diseases by topical application within the colon.