Background: M1a node involvement based on the 6th edition AJCC staging system was classified as regional node involvement in the 7th edition of esophageal squamous cell carcinoma (ESCC). However, the clinical significance of M1a node involvement based on the 6th edition staging system has not been well established. Thus, we analyzed the prognostic value of M1a node in patients of ESCC after definitive chemoradiotherapy (CCRT). Methods: A total of 188 ESCC patients had M0 disease based on the 7th edition AJCC classification, of which 31 (16.5%) of them were reclassified to the M1a patient group under the 6th edition AJCC classification. After definitive CCRT, we compared the basic characteristics of two groups, analyzed the rate of complete remission (CR), recurrence, finally assessed overall survival (OS), and disease-free survival (DFS) of each group. Results: Among 31 patients reclassified to M1a disease, 21 patients (67.7%) had subclavian nodes and 10 patients (32.3%) had celiac nodes. The median follow-up period was 18.3 months. The M1a group showed a significantly lower survival rate not only in median OS (M1a 16.4 months, M0 42.7 months, P = 0.015), but also in 5-year OS (M1a 10.8%, M0 41.2%). Three of 31 patients (9.7%) in the M1a group achieved CR, while 41 of 157 patients (26.1%) in the M0 group achieved CR (P = 0.048). However, there was no recurrence in the M1a group after achieved CR during follow-up period. Conclusions: Among ESCC patients after completing definitive CCRT, M1a patients according to the 6th AJCC staging system showed lower CR rate and OS rate compared with M0 disease patients. M1a nodes should be differentiated from regional node involvement.