We studied the efficacy of endoscopic ultrasonography (EUS) for malignant tumor of the digestive tract. Materials were 174 cases of gastric cancer, 15 cases of myogenic tumor, 22 cases of gastric malignant lymphoma and 37 cases of colon cancer. A radial sector type GF-UM2 and EUM2 (Olympus-Aloka) were used. Almost all walls of the digestive tract were observed as five layers by EUS, and each layer corresponded to the histological wall structure. Malignant lesions showed the characteristic ultrasonographic images, respectively. It was possible to diagnose easily the depth of tumorous invasion by the degree of wall destruction. Also, the internal structure of tumors could be observed by this method. Since EUS is a new examination which had added ultrasonographic diagnosis to conventional endoscopic diagnosis, the combination of endoscopic and EUS images has improved the accuracy of diagnosis.