Babies grunting while breastfeeding may be due to improper breastfeeding, minor pain, etc. 1. Improper breastfeeding: Problems including improper breastfeeding position, improper temperature and improper dosage can cause babies to feel uncomfortable while breastfeeding, and because babies can’t talk and express their dissatisfaction verbally, babies will grunt while breastfeeding. 2. Slight pain: if the baby’s mouth has mouth ulcers or trauma, when eating milk will touch the wound in the mouth, causing slight pain, but the baby is very hungry and want to eat milk, so there will be a baby grunting while eating milk phenomenon. Babies grunting while breastfeeding may also be related to other causes, we should promptly go to the regular hospital to identify the cause of the disease, and under the guidance of a professional doctor to choose the appropriate method of treatment.