Blood in the stool of newborns may be associated with allergic enteritis, vitamin K deficiency, necrotizing small bowel colitis and other causes. 1. Allergic enteritis: usually seen in formula-fed newborns, in contact with allergens, such as having milk protein allergy. The general mental state is good, usually accompanied by eczema and other allergic symptoms, mildly can appear in the stool with blood, the more serious can be seen in a large number of blood in the stool. 2. Vitamin K deficiency: newborns are born with unestablished intestinal flora or with congenital liver disease, and synthesize vitamin K insufficiently. It causes coagulation abnormality and tendency to bleeding, which may appear as blood in stool, skin purpura and other symptoms. 3. Necrotizing small intestinal colitis: bacterial colonization or intestinal ischemia and other causes, resulting in the destruction of the intestinal tract to produce mucus, leading to intestinal vulnerability to bacterial attack. It shows blood in the stool and may be accompanied by symptoms such as drowsiness and depression. When blood in stool occurs in newborns, it is recommended to consult a doctor for further examination, to clarify the cause with the help of the doctor, and to carry out targeted treatment or therapy.