Introduction Febrile seizuresare 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.