We report a patient with a neonatal seizure in whom diffusion-weighted imaging (DWI) at 8 days of age revealed high-intensity areas in the genu and splenium of the corpus callosum. The patient was a 2-day-old girl born at 39 weeks of gestational age. No apparent signs of asphyxia were found at birth. Clinically, she had a clonic seizure of the left hemisphere, with open eyes deviating to the left, and automatism around the mouth. The antiepileptic drug phenobarbital was administered once, her seizure was simultaneously stopped. Because she was a newborn, her corpus callosum was not completely myelinated. Intramyelinic edema was not responsible for these DWI findings; the mechanism of the abnormal DWI findings was clearly unknown. Here, we present abnormal DWI findings in the corpus callosum in a neonatal seizure case that did not meet all the criteria for neonatal hypoxic-ischemic encephalopathy (HIE).