We encountered a male infant with infantile Alexander disease presenting with megalencephaly and hydrocephalus as a neonate and subtle seizures at 3 months of age. At 6 months of age, bulbar paralysis appeared. Brain magnetic resonance imaging (MRI) showed abnormal findings with white matter involvement and a characteristic periventricular rim, satisfying the diagnostic criteria proposed by van der Knaap, except for MRI contrast. R239H mutation of glial fibrillary acidic protein gene was identified, representing a common cause of infantile-type Alexander disease.