In order to clarify the usefulness of EUS in the diagnosis of gastrointestinal carcinoid tumor, we examined 15 patients, who had carcinoid tumors of gastrointestinal tract (stomach: 5, duodenum: 2, rectum: 8), on the diagnosis in quality and depth by comparing endoscopical ultrasonography (EUS) with resected specimen. Carcinoid tumors of gastrointestinal tract were detected as homogenous hypoechoic tumors with sharp border in all site by EUS. Especially, it was characteristic that 14 of the 17 lesions (82%) which invaded into submucosa were mainly located in the third layer, and the second layer covered the tumor at the foot, and near the top, it touched the tumor and got indistinct. We decided the depth of invasion by comparing the hypoechoic tumor with normal structure of 5 layers. The accuracy rate was 88%. In conclusion, EUS was thought to be useful in the diagnosis and choice for treatment of carcinoid tumors of gastrointestinal tract.