The cause and mechanism of epilepsy after endoscopic third ventriculostomy (ETV) have still remained elusive. This single-center study aimed to explore and analyze the risk factors of post-operative seizure in pediatric patients with hydrocephalus undergoing ETV.Data of pediatric patients with hydrocephalus who were treated with ETV from October 1, 2015, to November 31, 2021, were retrospectively analyzed. Basic demographic characteristics, etiology of hydrocephalus, surgical details, and laboratory measurements were collected. An early postoperative seizure was defined as the occurrence of at least one clinical seizure within 24 h of ETV.A total of 50 participants were included in the study, of whom 5 (10.00%) cases were in postoperative epilepsy group and 45 (90.00%) cases were in non-epilepsy group. Epilepsy patients were younger than those without epilepsy, while no statistically significant difference was found (P = 0.0836). In the age subgroup, children with epilepsy were younger than 2 years old. All patients with epilepsy received Ringer's solution intraoperatively. The mean postoperative serum calcium and potassium concentrations were significantly lower in patients with epilepsy than in those without epilepsy (Pcalcium = 0.0429; Ppotassium = 0.0250). Moreover, a faster decrease of serum potassium and calcium levels was found in children with epilepsy compared with those without epilepsy after ETV.The decrease of serum calcium and potassium levels, younger age, and using Ringer's solution as irrigation fluid were risk factors for epilepsy after ETV.© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.