Background:Microscopic colitis (MC) encompasses collagenous and lymphocytic colitis and is diagnosed by histopathological changes of random biopsies which tacken from each segment of normal macroscopically colonic mucosae from patients who have chronic watery diarrhea of unknown etiology. Aims:Prevalence of microscopic colitis in patients with chronic watery diarrhea and have endoscopically normal colon . Materials and Methods:We prospectively enrolled 84 patients reviewed in ALASSAD and TISHREEN HOSPITALS between March 2015 until June 2016 .These patients were having watery diarrhea more than 3 times a day for more 4 weeks. Atotal 84 patients were enrolled for a total colonoscopy until terminal ileum . Two biopsies were obtained from all colonic segments and terminal ileum for diagnosed of microscopic colitis. On histopathologic examination, criteria for lymphocytic colitis (intraepithelial lymphocyte ≥ 20 per 100 surface epithelial cells, change in surface epithelium, mononuclear infiltration of the lamina propria) and collagenous colitis (subepithelial collagen band thickness ≥ 10 μm) were explored. Results:Microscopic colitis was diagnosed in 33 (39%)patients {22lymphocytic colitis,11collagenous colitis} . Female/Male: 15/18, mean age at diagnosis of microscopic colitis : 37 year, range: 20-69, the median duration of diarrhea: 9.5 monthes , the median number of bowel movements per day:5 times .And the common symptoms are: abdominal pain and flatulence. Conclusion :Biopsy of Syrian patients with the diagnosis of chronic watery diarrhea of unknown etiology and normal colonoscopic findings will reveal microscopic colitis in approximately 39% of the patients. Lymphocytic colitis is two times more frequent than collagenous colitis in these patients.