PURPOSE: This study was aimed to investigate the optimum dose of diazepam to reduce the recurrence of febrile seizures and side effects in children with febrile seizures. METHODS: The subjects of this study included 528 children with febrile seizures (3 months-5 years of age) who were admitted to Eulji University Hospital (Daejeon, Korea) from January 2008 to December 2011. The children divided into four groups according to the dose of diazepam; Group I, 121 patients, received no diazepam therapy, group II, 129 patients, received oral diazepam in a single dose of 0.1 mg/kg after the febrile seizures, group III, 127 patients, 0.2 mg/kg, and group IV, 151 patients, 0.3 mg/kg, respectively. RESULTS: Seizures recurred in 6 of 129 children (4.7%) in group II, 1of 127 children (0.8%) in group III, and none of 151 children in group IV recurred. For the 121 untreated patients, febrile seizures recurred in 20 (16.5%) children. This study revealed a significant difference in the rate of recurrence of febrile seizures between children treated with diazepam and those who were not. And the recurrence rate was decreased by the increment of the dosage of diazepam, but there was no significant difference between groups. The side effects were observed in 19.9% of children treated with diazepam, 3.9% in group II, 12.6% in group III, and 39.7% in group IV, The rate of side effect was also increased with the increment of the dosage. CONCLUSION: An oral diazepam therapy will reduce the incidence of recurrent febrile seizures during the same febrile illnesses. We think the optimum dose of diazepam is 0.1 mg/kg or 0.2 mg/kg rather than 0.3 mg/kg. However, the use of oral diazepam after a febrile seizure should be carefully considered with weighing the benefits and potential adverse effects.