Objective To investigate the cranial magnetic resonance imaging（MRI） characteristics of children with febrile infection-related epilepsy syndrome（FIRES）. Methods A retrospective analysis was performed for the imaging characteristics of children with FIRES who were admitted to Department of Pediatrics，Peking University First Hospital，from November 2020 to August 2024，including the characteristic manifestation of claustrum sign on cranial MRI. Results A total of 86 children with a confirmed diagnosis of FIRES were included，among whom there were 65 boys（75.6%） and 21 girls（24.4%），with a median age of onset of 6.35（4.4，8.32） years. Among these children，14（16.3%） had normal cranial MRI findings in the acute stage，with T2 FLAIR changes as the most common abnormal manifestation（39.5%），and 30 children（34.9%） experienced brain atrophy，with a median time of 44（34，72） days for the onset of brain atrophy for the first time. There were 22 children（25.6%） with positive bilateral claustrum sign on cranial MRI，which manifested as symmetrical T2 FLAIR hyperintensity with limited diffusion in the bilateral claustrum，and the median time to the first appearance of claustrum sign was 11（7，15） days，while the median time to negative conversion of claustrum sign was 33（24，50） days. The claustrum sign disappeared after the relief of status epilepticus in the acute stage in most children. Among the children in this study，71 entered the chronic stage during follow-up，3 had normal cranial MRI results during the course of the disease，and 34 had brain atrophy for the first time in the chronic stage，with a median time of 186（115，429） days to the first appearance of brain atrophy on cranial MRI，while of all 86 children，64（80.0%） experienced brain atrophy on cranial MRI in the acute stage and the chronic stage. Conclusion Children with FIRES have diverse cranial MRI characteristics. There might be normal MRI manifestations at the beginning of the disease，and positive bilateral claustrum sign might be the specific manifestation in the acute stage. Changes in the claustrum disappear after the relief of status epilepticus in most cases，and most patients may progress to brain atrophy in the chronic stage.