Colitis can make stools thinner, but the probability of occurrence is small, and there are various reasons for thinner stools. Common symptoms of colitis are abdominal pain, diarrhea, bloating, mucus, pus and blood stools, and occasionally constipation and difficulty in defecation. Stool thinning can occur when there is colonic contracture or internal colonic mass in colitis, and the probability of this symptom occurring is very small. There are many reasons for the thinning of stool, usually the internal diameter of the rectum and anus determines the thickness of stool, and the thinning of stool is usually related to rectal tumors, rectal polyps, hemorrhoids; there are also part of the thinning of stool is caused by dietary structure changes and other non-pathological reasons. If there is colitis or symptoms of thinning stool, it is recommended to consult a doctor in a timely manner, under the guidance of the doctor to clarify the cause, to avoid delaying the condition.