An infant’s fontanel closing at six months is generally considered abnormal. The fontanel is divided into anterior and posterior fontanelles. The posterior fontanel is small or closed at birth, and closes at the latest around 6 to 8 weeks of age. The anterior fontanel is about 1-2 cm at birth and increases in size as the skull grows, gradually ossifying and becoming smaller around 6 months of age and closing by 2 years of age at the latest. The fontanel is often used clinically to assess cranial development. Therefore, it is not normal for the fontanel to close at six months, which may be caused by microcephaly, congenital brain dysplasia, genetic metabolic disease, etc. There may be other reasons for the closure of fontanel at six months, so parents are advised to take their babies to the doctor as soon as possible for a clear diagnosis and treatment.