Four-month-old baby half a day without urination is physiological, may also be acute glomerulonephritis and other pathological factors. 1. physiological factors: if the baby’s milk intake is not enough, resulting in a decrease in urine volume caused by half a day without urine. Physiological factors lead to half a day without urination, usually after the recovery of milk volume can be restored on their own. 2. Acute glomerulonephritis: four months baby urinary system and immune system is still developing, easy to get infected with bacteria or viruses. If infected with group A beta-hemolytic streptococcus, EBV, etc. can cause acute glomerulonephritis leading to a decrease in the baby’s urine output. Four-month-old baby half a day without urine, there may be other reasons, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.