Acute disseminated encephalomyelitis (ADEM) is a rare, postinfectious autoimmune inflammatory demyelinating disease of the central nervous system. ADEM presents clinically encephalopathy in association with polyfocal neurologic deficits. Of them, optic neuritis is less common symptom. We experienced ADEM with optic neuritis associated with Mycoplasma pneumoniae infection in a 5 year-old girl. She initially presented lethargy, irritability, ataxia and loss of pain sense on right hand and progressed to decreased visual acuity and papilledema of both eyes on the 4th hospital day. Brain magnetic resonance imaging showed multiple bilateral hyperintense lesions in the subcortical white matter on T2 weighted images. After administration of intravenous immunoglobulin and high dose intravenous methylprednisolone, she recovered completely.