A 5-year-old boy with left side optic neuritis, which manifested itself 21 days after the onset of rubella eruption, is reported. Seven days after the onset of rash which persisted for 3 days, he was found to be excessively somnolent and disoriented, and a diagnosis of rubella encephalitis was made at our clinic. Clinical symptoms spontaneously subsided 3 days later. Twenty-one days after the appearance of rash (16 days after the onset of encephalitis) he complained of left frontal headache and blurred vision of left eye. The funduscopic examination revealed the left papillitis. Pattern reversal VEP (PVEPs) evoked by stimuli of left eye showed absence of N75 wave, and a prolonged conduction time and low amplitude of P100 wave. Corticosteroid therapy improved his complaints, funduscopic and PVEPs findings. When the treatment was stopped, the funduscopic findings were exacerbated but were improved soon again by the additional corticosteroid therapy. A delayed onset of optic neuritis after the initial infection and a prompt response to corticosteroid therapy may suggest an involvement of some autoimmune process in the pathogenesis of postinfectious optic neuritis in our case.