Respiratory syncytial virus (RSV) is a cause of neurological complications in infants. We report a rare case of RSV encephalopathy in an infant who presented with poor sucking and hypothermia at 17 days of age after suffering from rhinorrhea and a cough for several days. After hospitalization, the patient presented with stupor and hypotonia lasting for at least 24 h, and was intubated, sedated, and ventilated for treatment of pneumonia. These symptoms led to diagnosis of pediatric systemic inflammatory response syndrome (SIRS) caused by RSV infection. High-dose steroid therapy was combined with artificial ventilation because the initial ventilation therapy was ineffective. Interleukin (IL)-6 levels in spinal fluid were markedly increased upon admission, and serum IL-6 and IL-8 levels showed even greater elevation. The patient was diagnosed with RSV encephalopathy. On day 5, high signal intensity in the bilateral hippocampus was observed on diffusion-weighted magnetic resonance imaging (MRI). On day 14, the patient presented with delayed partial seizure and an electroencephalogram showed occasional unilateral spikes in the parietal area, but the hippocampal abnormality had improved to normal on MRI. (99m)Tc-labeled ethylcysteinate dimer single-photon emission computed tomography (SPECT) on day 18 showed hypoperfusion of the bilateral frontal and parietal regions and the unilateral temporal region. SPECT at 3 months after onset still showed hypoperfusion of the bilateral frontal region and unilateral temporal region, but hypoperfusion of the bilateral parietal region had improved. The patient has no neurological deficit at 6 months. These findings suggest that RSV encephalopathy with cytokine storm induces several symptoms and complications, including SIRS and prolonged brain hypoperfusion on SPECT.