Weight is an important indicator of growth and development of infants, and the rate of weight gain varies from month to month. Therefore, the normal weight gain each month should be judged in conjunction with the age of the baby, such as an increase of about 1 to 1.7 kg in the first month after birth is considered normal. Weight is easy to measure accurately and is the most readily available indicator of a baby’s growth and nutritional status. An infant’s weight is closely related to his/her feeding, nutrition, and illness. Infants’ monthly weight gain varies and is not equal, so the normal monthly weight gain needs to be judged in relation to the age of the baby. For example, the weight gain of a normal full-term infant is usually about 1~1.7kg in the first month after birth, about twice the birth weight in the third to fourth month after birth, with a monthly increase of about 1kg, and the weight gain in the first three months of a year is about the same as the weight gain in the last nine months, with a monthly increase of about 0.5kg. It is recommended to consult a specialist for a comprehensive assessment and judgment.