BACKGROUND/AIMS: Endoscopic submucosal dissection (ESD) has been accepted as a standard treatment of early gastric cancer (EGC). However, the indication of ESD in undifferentiated-type EGC was controversial. The aim of this study was to evaluate the therapeutic outcomes of ESD in undifferentiated-type EGC according to expanded indication. METHODS: At Soonchunhyang University Bucheon Hospital, a total of 82 lesions in 81 patients with undifferentiated-type EGC were treated with ESD. The therapeutic outcomes of ESD were evaluated by resection method (en bloc resection; piecemeal resection), histologic curative resection, complications and recurrence rates after ESD. RESULTS: The rate on en bloc resection and complete resection rate were 87.8% (72/82) and 80.5% (66/82), respectively. In signet ring cell carcinoma, the complete resection rate was higher than those in poorly differentiated adenocarcinoma and poorly differentiated adenocarcinoma with signet ring cell features, but there was no statistical significance (89.3% vs. 75.0%, 76.7%; p=0.347). The lateral margin positivity rate in poorly differentiated adenocarcinoma, signet ring cell carcinoma and poorly differentiated adenocarcinoma with signet ring cell features were 12.5%, 3.6% and 13.3%, respectively (p=0.395). The vertical margin positivity rate were 12.5%, 3.6% and 10.0%, respectively (p=0.485). The overall recurrence rate was 3.0% during a mean follow-up period of 37.4 months. CONCLUSIONS: ESD may be considered as a feasible treatment for undifferentiated-type EGC according to expanded indication. The therapeutic outcome of ESD in undifferentiated-type EGC is likely to be favorable, though further longer follow-up studies are needed.