21 days newborn two days no stool, can be physiological phenomenon, can also be constipation, congenital megacolon and other pathological phenomena, can be taken general treatment, lactulose oral solution and other medications, surgical treatment and so on. 1. Physiological factors: breastfed newborns due to less food residue, may lead to decreased frequency of defecation, commonly known as saving belly. At this time, the child does not have defecation effort, fart odor, abdominal distension and other discomfort, the amount of milk is also normal, usually do not need special treatment. Insufficient feeding can also lead to newborns two days without stool, should be increased moderately, such as milk. 2. Constipation: Constipation is usually accompanied by symptoms such as decreased stool frequency, smelly farts, straining to defecate and bloating. Probiotics can be used to regulate the condition, such as Bacillus subtilis Dictyostelium granules. 3. Congenital megacolon: It is one of the most important causes of persistent constipation. It can cause the newborn to have no bowel movement for up to a week or two, while oral medication is not effective. At this point, a surgeon is needed to evaluate the need for surgery. The 21-day newborn did not have a bowel movement for two days, there may be other reasons such as intestinal obstruction, it is recommended to consult a doctor in a timely manner, to rule out abnormalities, if necessary, with the doctor’s treatment, the doctor’s medication needs to be used under the guidance of the doctor.