A previously healthy 3-year-old girl was admitted to the Department of Pediatrics in Severance Hospital with sudden symptoms of melena. The vital signs were stable, and splenomegaly was found in a physical examination. The patient had moderate thrombocytopenia. There was no evidence of autoimmune disease. A upper gastrointestinal endoscopy and esophagogram showed a varix on the lower esophagus. Coarse liver parenchymal echoes and increased periportal echogenicity were seen on a Doppler sonogram. The velocity of the portal vein mildly increased. Magnetic-resonance-cholangiopancreatogram (MRCP) demonstrated normal portal structures. A sono-guided liver biopsy was performed, but the pathological findings were unremarkable. Based on these findings, we diagnosed the patient with idiopathic portal hypertension. The patient was discharged and was treated with oral beta blocker. We report a case of idiopathic portal hypertension with a brief review of the literature.