Febrile seizures (FS) are recognized as an antecedent to the development of temporal lobe epilepsy with hippocampal sclerosis (TLE-HS), but it is unclear whether prolonged FS are a direct cause of TLE-HS. Here, we used a rat model of infantile FS to study the effects of inflammatory cytokines on seizure susceptibility and neuronal death in adults. Prolonged hyperthermia-induced seizures (pHS) were induced in male Lewis rats at post natal day (P) 10. Cytokines were administered twice intranasally, once immediately after pHS and once the following day. The effects of intranasal interleukin (IL)-1β or tumor necrosis factor (TNF) α were tested in rats undergoing a single episode of pHS (P10) and in rats undergoing repeated pHS (P10 and P12). Seizure susceptibility was tested at P70-73 by quantifying the seizure onset time (SOT) after kainic acid administration, and neuronal cell injury and gliosis in adulthood. SOT significantly reduced in rats receiving IL-1β together with repeated pHS, whereas no significant effects were seen in rats receiving IL-1β after a single pHS episode, or in rats receiving TNFα. Hippocampal neuronal cell loss was observed in the CA3 region of rats receiving IL-1β together with repeated pHS; however, there was no significant change in gliosis among each group. Our results are consistent with the hypothesis that excessive production of IL-1β after repeated prolonged FS can enhance adult seizure susceptibility and neuronal cell death, and might contribute to the development of TLE-HS.