In this study, we investigated a short-term outcome of 56 cases of ESD for early gastric cancer performed in our department concerning the tumor diameter within or over 20 mm. Seventeen lesions were larger than 21 mm (large group), and 39 lesions were within 20 mm (indication group). There was no significant difference in the background factors between the two groups. The mean operating time and median of post operative hospital stay of the large group were longer than those of the indication group, and those differences were statistically significant. On the other hand, no significant difference was seen in the rate of one-piece resection, the incidence of complications and curability. With a further improvement of our skills, an ESD application in a case where the tumor diameter is larger than 21 mm may be extended.