Thin stool with fishy smell does not necessarily mean intestinal cancer. There are many reasons for thin and fishy stools, which may be caused by intestinal infection, indigestion, gastrointestinal bleeding and other reasons. When intestinal infection occurs, bacteria invade the intestine and the pathogenic bacteria are wrapped and engulfed by inflammatory cells, leading to the death of a large number of inflammatory cells and thus expelled from the body, causing fishy smelling stools. When the patient has indigestion, a large amount of food is not completely digested in the stomach, which makes the food residue in the intestine to rot, causing a fishy smell, especially after eating protein-based food. However, if the thin and fishy stool is accompanied by black stool, it is necessary to pay attention to the possibility of gastrointestinal bleeding or even intestinal tumor, especially malignant tumor. Since the tumor destroys the mucosal tissue in the intestine, thus causing its necrosis and discharge, thin fishy-smelling stools appear. At this time, patients need to go to the Department of Gastroenterology for gastroenteroscopy in time to make a clear diagnosis. If it is caused by irritable bowel syndrome or enteritis, symptomatic treatment with drugs is sufficient. However, if it is caused by intestinal cancer, surgery should be the main treatment, together with chemotherapy and radiotherapy.