A 10-month-old baby’s sudden decrease in urine output may be caused by physiological reasons, diarrhea, acute glomerulonephritis and other reasons. 1. physiological reasons: due to the baby too little milk, drink less water, sweating more causes baby suddenly reduce urine, give the baby to replenish enough water after the urine volume can increase. 2. Diarrhea: baby’s immunity is poor, easy to intestinal infections, causing diarrhea. Diarrhea leads to excessive discharge of water from the feces, resulting in insufficient blood volume in the baby’s body, causing a decrease in urine output. 3. Acute glomerulonephritis: baby acute nephritis, due to glomerular capillary endothelial cell hyperplasia will lead to acute glomerular filtration function is reduced, resulting in renal insufficiency, caused by the decrease in urine volume. Other causes of sudden decrease in urine output in 10-month-old babies include serious infections and other causes. To the baby to supplement the water after the urine volume does not increase, parents should promptly take the child to the regular hospital to improve the examination, clear cause of the disease to give targeted treatment.