background: Febrile seizures are the most frequent convulsive episode in children, involving 2-5% of those between the ages of six months and five years. Arginine-vasopressin (AVP), a pituitary hormone, has been shown to play a role in response to fever and convulsions, affecting the thermoregulatory system. Copeptin's C-terminal region has been identified as a reliable predictor of AVP production. Objective: The aim of the current study was to assess serum copeptin's diagnostic utility in febrile seizures. Patients and methods: A case-control study was conducted at Zagazig University’s Emergency Room and Neurology Unit of Children’s Hospital. A total of 46 patients were recruited and were divided into two groups; Febrile seizure group included 23 patients and febrile without seizures group included 23 patients. Results: There is significant higher copeptin value in febrile seizures group compared to febrile control without seizures group (P<0.05). Copeptin in diagnose seizure patients in febrile patients revealed a sensitivity of 82.6%, a specificity of 78.3% and 80.4% accuracy at a cutoff value >75 pg/ml. Conclusion: Serum copeptin can tell the difference between a febrile seizure and a febrile without a seizure. Serum copeptin at cut off value >75pg/ml was a good marker for detecting seizures in febrile patients. Serum copeptin performed adequately as a diagnostic tool, highlighting its potential role in the febrile seizure diagnostic algorithm. Keywords: Serum Copeptin, Febrile Seizures, Children, Case control study, Zagazig University.