Gastric teratoma is an extremely rare neoplasm in children which account for less than one percent of all teratomas. Unlike other teratomas, most reported gastric teratomas was benign except one case and occurred predominantly in boys. Additionally, gastric teratomas present in the first year of life as a palpable mass, abdominal distension, vomiting, hematemesis or respiratory distress. Patients with gastric teratomas have an excellent prognosis after complete excision of the tumor. We report a case of immature gastric teratoma in an one-day-old boy, which was diagnosed by abdominal sonography and CT scan, and confirmed by surgery.