A baby with low urine output is defined as less than 200 ml of urine in 24 hours. Decreased urine output in babies may be a physiologic phenomenon, such as decreased water intake. It may also be due to pathologic causes such as water loss and glomerulonephritis. 1. Physiological phenomenon: physiological oliguria can be caused by insufficient water intake or excessive sweating recently. Physiologic oliguria can be normalized by supplementing water intake, so no special treatment is needed. 2. Pathological oliguria: caused by severe water loss, blood loss, acute glomerulonephritis, nephrotic syndrome, etc. At this time, it is necessary to supplement fluids to correct dehydration. (1) Severe water loss and blood loss: it will cause insufficient effective circulating blood volume and lead to pathologic oliguria. (2) Acute glomerulonephritis: the disease will lead to a decrease in the glomerular filtration rate, which will not be able to expel excess water from the body, and oliguria will occur. (3) nephrotic syndrome: the disease will lead to renal function damage, but also accompanied by a decrease in effective circulating blood volume, patients with a large amount of proteinuria loss, causing sodium and water retention, resulting in oliguria. Babies who urinate less, should promptly go to the hospital pediatrics, identify the cause should be under the guidance of the doctor for treatment.