Blood in stool of rectal cancer belongs to irregular blood in stool, which is not regular and it is impossible to determine how often it occurs. The occurrence of blood in stool of rectal cancer patients is usually related to the patients’ defecation and the ulceration of rectal tumor. In the early stage, some patients may not have obvious blood in stool, but some patients may have intermittent blood in stool; as the condition develops and aggravates, the tumor gradually increases in size, and the ulceration of cancerous tissues also occurs frequently, and the situation of blood in stool will also be frequent gradually. Blood in stool of rectal cancer patients is also related to defecation. If the patient’s stool is soft, blood in stool may not occur during defecation; however, if the patient’s stool is dry, it will cause friction and stimulation to the surface of tumor, which will lead to blood in stool. Once rectal cancer patients are diagnosed, they should go to the hospital for reasonable treatment in time to avoid aggravation of the condition and endangerment of life.