Collagenous colitis is a newly recognized disease that causes chronic watery diarrhea and occurs predominantly in middle aged woman. Radiologic and endoscopic examination of the colon are usually normal, therefore diagnosis must be associated with some autoimmune diseases and medication history of certain drugs, The involvement of collagenous colitis is mainly in large intestine but rarely occurs in both large and small intestine. A 36 years old female presented with a 5-month history of watery diarrhea and weight loss. She had a past medical history of rheumatoid arthritis. Multiple biopsies of colonic mucosa revealed a nonspecific findings. Jejunal biopsy showed subepithelial band of collagen deposition that was compatible to collagenous colitis. Some improvement of symptoms occurred with prednisolone therapy. Hence, we present the first case of collagenous enteritis with histologic evidence of intestinal involvement.