We describe a case of gastric aberrant pancreas with acute pancreatitis followed up with subsequent endoscopic ultrasound. A 20-year-old woman known to have aberrant pancreas in the stomach was admitted to our hospital because of severe epigastralgia. Laboratory tests showed slight C reactive protein elevation without hyperamylasemia. Esophagogastroduodenoscopy revealed a swollen submucosal lesion (SML) to a greater degree compared with the previous findings. Subsequent endoscopic ultrasonography (EUS) revealed a swollen lesion of 35 mm in diameter. The internal echo-pattern was more hypoechoic than in the previous EUS. The border between the fourth layer (muscularis propria) and the SML was unclear. The anechoic lumen in the mass, considered as the ductal lumen, was dilated. Based on these results, we diagnosed the patient as having acute inflammation, resembling pancreatitis, in the aberrant pancreas.