We herein report a rare case of very small Barrett's adenocarcinoma. A 65-year-old man underwent surveillance esophagogastroduodenoscopy (EGD) 3 years after endoscopic submucosal dissection (ESD) for superficial Barrett's adenocarcinoma, which revealed a very small reddish area in the mucosa, 2 mm in diameter, in long-segment Barrett's esophagus. The EGD carried out 1 year later confirmed slight enlargement of the lesion, from 2 mm to 3 mm in diameter. Macroscopic type changed from flat type to slightly depressed type. On narrow-band imaging with magnifyingendoscopy, an irregular microstructure and irregular microvasculature became recognizable. It was resected by ESD and diagnosed as mucosal adenocarcinoma with a diameter of only 3 mm.