Objective To investigate the diagnostic value of conventional endoscopy (CE) and endoscopic ultrasonography (EUS) for invasion depth prediction of superficial gastric cancer. Methods A total of 84 patients with superficial gastric cancer underwent both CE and EUS before treatment at Beijing Shijitan Hospital from January 2011 to December 2019. The patients were divided into CE affirmation group (47 cases) and CE non-affirmation group (37 cases) according to the endoscopist's affirmation in the results of CE. Diagnostic accuracy of each method was compared with the histology of the resected specimen. And influential factors for the diagnosis were analyzed. Results The overall accuracy in determining the invasion depth of superficial gastric cancer was 73.8% (62/84) for CE and 81.0% (68/84) for EUS respectively (P=0.092). In CE affirmation group, the diagnostic accuracy of CE was significantly higher than that in the CE non-affirmation group [93.6% (44/47) VS 48.7% (18/37), χ2=21.656, P<0.001]. Twenty (23.8%) of 84 lesions were over-staged by CE, dignosed as surgical candidates, and 8 (40.0%) of the over-staged diagnosis were modified by additional EUS assessment. Multivariate logistic analysis showed that influential factors associated with observer affirmation included uneven surface of lesion (OR=5.076, 95%CI: 1.628-15.821, P=0.005), margin elevation (OR=3.831, 95%CI: 1.238-11.857, P=0.020) and undifferentiated carcinoma (OR=6.887, 95%CI: 1.882-25.204, P=0.004). Conclusion For patients of CE affirmation in the invasion depth, the diagnostic accuracy is high. For those of non-affirmation, additional EUS can improve the diagnostic accuracy and help to develop a more appropriate regime.