Acute transverse myelitis is a focal inflammatory disorder of the spinal cord, resulting in motor, sensory, and autonomic dysfunction which would be the initial manifestation of acute disseminated encephalomyelitis. A 7-year-old boy developed weakness of lower extremities associated with dizziness and urinary dysfunction after upper respiratory infection. He showed gradual decreased mental status with respiratory difficulty. Spinal MRI showed diffuse spinal cord swelling from C3 to C7 levels with high signal intensity lesion on T2-weighted image, which is involved central gray matter of spinal cord from C3 to C7, proximal portion to cervicomedullary junction, and distal portion to the cornus medullaris. After the supplement of high dose intravenous methylprednisolone therapy with ventilator care, he showed gradual improvement. The brain MRI after extubation showed multifocal high signal intensity lesions in bilateral cerebral white matter on axial T2-weighted image. Immunoserologic test(neutral antibody test) for enterovirus 71 was positive. Dysfunction of the bladder lasted for 33 days. We report a case of transverse myelitis which progressed to acute disseminated encephalomyelitis by enterovirus 71 in a 7-year-old boy with related literatures.