BACKGROUND: Treatment strategies for superficial esophageal squamous cell carcinoma (SESCC) are determined mainly on the basis of the invasion depth. The Japan Esophageal Society (JES) developed a simplified magnifying endoscopic classification for estimating the invasion depth of SESCC. We aimed to evaluate its accuracy. METHODS: We prospectively applied the JES classification for estimating the invasion depth of SESCC to 204 consecutive lesions from 6 hospitals in Japan between April 2016 and October 2018. We analyzed the accuracy of the endoscopic diagnosis by adding the following two categories to the JES classification: ≥ 7 mm lesion in B2 vessels (defined as B2 ≥ 7 mm) and B2 vessels with inflammation (defined as B2i). RESULTS: After applying the exclusion criteria, 201 lesions remained in the analysis. The diagnostic value of type B1, B2, B3 vessels were as follows: sensitivity, 93.9%, 68.0%, 25.0%; specificity, 81.1%, 89.2%, 99.4%; positive predictive value (PPV), 95.6%, 47.2%, 75.0%; negative predictive value (NPV), 75.0%, 95.1%, 95.4%; and accuracy, 91.5%, 86.5%, 95.0%, respectively. A retrospective analysis showed that the diagnostic accuracy was higher in type B2 vessels (86.5% to 92.0%). An avascular area (AVA) was found in 55 (27%) of the 201 lesions, which tended to be associated with a deeper pathological diagnosis of each Type B vessel. In an additional analysis, B2 ≥ 7 mm and B2i improved the diagnostic accuracy of type B2 vessels from 86.5% to 92.0%. CONCLUSIONS: The JES classification is useful for estimating the invasion depth of SESCC. The diagnostic accuracy for type B2 vessels was low, which may be improved by using B2 ≥ 7 mm and B2i.