There are two main reasons why a four-month-old baby does not gain weight: first, feeding factors; second, disease factors. Feeding factors may be due to the lack of quality of mother’s breast milk for breastfed children, the child’s nutritional intake is not enough, so it will lead to weight does not grow. If a formula-fed child, consider the energy of formula feeding or should be replaced with the next stage of formula, parents did not give timely replacement, the child’s intake of formula calories is not enough, will also lead to the baby’s weight does not increase. For disease factors, such as the baby always suffers from gastrointestinal function indigestion, often bloating, diarrhea, etc., or the baby suffers from a decline in immune function, causing respiratory diseases, often treated with drugs, can lead to the child’s nutrient absorption disorders, resulting in weight does not grow.