We judged the efficacy of chemotherapy using endoscopic ultrasonography (EUS) in 26 cases of gastric cancer. Treatment efficacy was evaluated according to the General Rules for the Gastric Cancer Study, based on the reduction of the largest cross-sectional area of the tumor. A reduction of over 50% was rated as U-PR and a reduction of -25 ?? 50% was rated as U-NC. Our findings showed U-PR in 11 cases and U-NC in 15 cases. Three cases initially considered to be NC according to the rules were judged to be U-PR based on EUS findings. Marked therapeutic efficacy in these 3 cases was demonstrated clinically and this was confirmed by EUS findings. Generalized Wilcoxon test showed a significant difference in the cumulative survival rate between U-PR and U-NC cases (p<0.05). EUS provides an objective means of evaluating the efficacy of chemotherapy in gastric cancer patients, including those with lesions that cannot be evaluated by the General Rules for the Gastric Cancer Study.