Sometimes square and sometimes round stools may be related to diet, which is a normal phenomenon; it can also be seen in pathological reasons, such as intestinal tumors, anal canal diseases and so on. 1. Physiological reasons: the shape of stool is closely related to the food we eat, which affects the peristalsis of gastrointestinal tract and the composition of feces, and the different food we eat may lead to sometimes square and sometimes round stools. 2. Intestinal tumors: the more common symptoms of intestinal tumors are change of bowel habit and change of stool shape. Intestinal tumors can protrude into the lumen, resulting in narrowing of colorectal lumen, which causes change of stool shape, sometimes square and sometimes round. 3. Anal canal diseases: for example, hemorrhoids, anal fissure, etc., the narrowing of anal opening can cause the change of stool character, which can be sometimes square and sometimes round. Sometimes the stool is square and sometimes round, except physiological reasons, should go to the hospital to find out the cause according to the cause of treatment.