Introduction : Valproate is one of the widely used antiepileptic drugs. Despite the safety of valproate, it can also cause some serious adverse effects, such as a pancreatitis. Etiology is not discovered yet, but reports are surging that 13% of regular valproate user has experienced some sort of pancreatitis. We report a case of severe pancreatitis with pseudocyst in a 5-year-old boy treated with valproate for epilepsy. Case : A 5-year-old boy with language developmental delay visited at our emergency room due to lethargy and vomiting. He also had high fever and abdominal cramping. He was taking valproate (28mg/kg/day bid) for epilepsy for four months. On physical examination, he had periumbilical and right upper quadrant tenderness. His serum amylase and lipase were significantly raised (336 U/L and 1159 U/L, respectively). His abdominal ultrasound showed diffuse pancreatic swelling, large amount of fluid collection in perihepatic, perisplenic and pelvic cavity. We treated him with supportive care, and changed his medications from valproate to levetiracetam. After five days, clinical symptoms were improved. After 12 days, his follow up computerized tomography images showed remained swelling of the pancreas, and newly identified cystic mass with a size of 6 x 4 cm in prepancreatic area, which assumed to be contained with acute necrotic fluid collection. We decided to have close observation, instead of immediate surgical intervention. After 17-day admission, He was discharged with recovery state. After discharge, we performed magnetic resonance cholangiopancreatography 48-days after first onset. The result showed no bile duct anomaly, improved swelling and decreased fluid collection from 6.0x4.0cm to 2.0x1.0cm size. After five months, He was stable and follow up ultrasound showed normal pancreas and resolution of pseudocyst . Conclusion : Valproate can occur pancreatitis and dose or period of medication seems to be not a determinant for its occurance. Therefore, suspicion for acute pancreatitis seems necessary when valproate user complains nausea, vomiting or severe abdominal pain. The authors report a case of valproate induced pancreatitis with pseudocyst formation in a child with epilepsy.