To determine the utility and limitations of an ultrasonic miniprobe (UMP) in the staging of gastric cancer, we evaluated 46 patients who underwent endoscopic ultrasonography (EUS) using an UMP and who were histologically determined to have gastric cancers. In every case, UMP findings were compared with histopathological findings after treatment. The total accuracy of UMP relative to the depth of tumor invasion was 71.7% (33/46 cases). Accuracy with respect to T1-m tumor diagnosis was 75.7% (22/29 cases), and for T1-sm, 76.9% (10/13 cases), but accuracy for T2 tumor diagnosis was low, due to ultrasound attenuation. When the analysis was carried out based on the size of tumor, the accuracy for UMP was 50.0% (9/18 cases) for all tumors over 20 mm and 85.7% (24/28 cases) for all tumors smaller than 20 mm. We conclude that UMP is suitable for investigation of tumor extension when the lesion is superficial and/or small gastric cancers which do not cause ultrasonic attenuation, but not when the tumor is large or located in certain sites, although conventional EUS is useful in some of these cases.