The posterior fontanelle is usually very small at birth or already closed, and closes at the latest about 6-8 weeks after birth. The posterior fontanelle is composed of the bone gap between the parietal bone and the occipital bone, and is triangular in shape, as it is not supported by the skull and is directly connected to the meninges and brain tissue under the scalp. Under normal circumstances, the posterior fontanelle is very small at birth and usually closes in about 6-8 weeks, and the time of closure is also related to growth and development. In children with some diseases, such as cerebral hypoplasia and congenital hydrocephalus, the closing time of the posterior fontanelle may be prolonged or even not closed, so early detection and treatment are needed. Parents need to be cautious when caring for their infants because the fontanelle is at the back of the head. They should avoid using pillows made of too hard material to avoid deformation of the infant’s head and should avoid sharp objects to prevent damage to the head.