Purpose: Additional surgery is commonly recommended in gastric cancer patients who have a high risk of lymph node metastasis or a positive resection margin after endoscopic resection. We conducted this study to determine factors related to residual cancer and to determine the appropriate treatment strategy. Materials and Methods: A total of 28 patients who underwent curative gastrectomy due to non-curative endoscopic resection for early gastric cancer between January 2006 and June 2009 were enrolled in this study. Their clinicopathological findings were reviewed retrospectively and analyzed for residual cancer. Results: Of the 28 patients, surgical specimens showed residual cancers in eight cases (28.6%) and lymph node metastasis in one case (3.8%). Based on results of the endoscopic resection method, the rate of residual cancer was significantly different between the en-bloc resection group (17.4%) and the piecemeal resection group (80.0%). The rate of residual cancer was significantly different between the diffuse type group (100%) and the intestinal type group (20%). The rate of residual cancer in the positive lateral margin group (25.0%) was significantly lower than that in the positive vertical margin group (33.3%) or in the positive lateral and vertical margin group (66.7%). Conclusions: We recommended that patients who were lateral and vertical margin positive, had a diffuse type, or underwent piecemeal endoscopic resection, should be treated by surgery. Minimal invasive procedures can be considered for patients who were lateral margin positive and intestinal type through histopathological examination after en-bloc endoscopic resection.