Background: The prediction of invasion depth is important to decide the treatment modality for the undifferentiated type early gastric cancer (EGC) when size is less than 2 cm and had no ulceration. We aimed to identify the endoscopic features associated with submucosal invasion in the undifferentiated type EGC that meet the criteria of size and status of ulcer in the endoscopic submucosal dissection (ESD). Methods: A total of 120 patients with undifferentiated type EGC who received ESD or operation from August 2008 to December 2017 were enrolled in this study. All lesions met the ESD criteria except the invasion depth. We retrospectively reviewed endoscopic features of tumor before the resection and depth of invasion after resection. Results: In 120 undifferentiated EGCs, the mucosal and submucosal cancer were 97 and 23 lesions, respectively, In univariable analysis, discolor change, upper third location, the presence of deep/wide erosion were associated with submucosal invasion. Multivariable analysis revealed that upper/middle third location (odds ratio [OR] 8.0, 95% confidence interval [CI] 1.2-55.0; OR 7.9, 95% CI 1.8-35.1), erosion or polypoid (OR 41.8, 95% CI 4.1-427.9), and elevated type (OR 20.9, 95% CI 2.5-173.8) were significant risk factors. In 112 patients received gastrectomy with lymph nodes dissection, lymph node metastases were found in four cases (three mucosal cancer and one submucosal cancer). However, there was no lymph node metastasis in the lesions meeting the expanded ESD indication. Conclusions: The careful decision of treatment modality is needed for undifferentiated type EGC with erosion or elevated gross type located on the upper/middle third, although the tumor size and ulcer status meet the ESD indication.