Background: The American Joint Committee on Cancer (AJCC) 8th Edition Cancer Staging System was implemented in 2018; however, it has not been validated in an Asian melanoma population. Objective: The purpose of this study was to validate the new system using a cohort of Japanese melanoma patients. Methods: The AJCC 7th and 8th Editions were used for TNM classification of patients in a database established by the Japanese Melanoma Study Group. Patient data with sufficient information to be applicable to the AJCC 8th staging were selected. The Kaplan–Meier method was used to estimate disease-specific survival and relapse-free survival. Results: In total, data for 3097 patients were analyzed. The 5-year disease-specific survival according to the 7th and 8th Edition staging system were as follows: IA = 98.5%/97.9%; IB = 95.4%/96.2%; IIA = 94.2%/94.1%; IIB = 84.6%/84.4%; IIC = 72.2%/72.2%; IIIA = 76.2%/87.5%; IIIB = 60.7%/72.6%; IIIC = 42.0%/55.3% and IIID = none/26.0%. The 5-year relapse-free survival according to the 7th and 8th Edition staging was as follows: IA = 94.5%/92.7%; IB = 85.4%/85.3%; IIA = 80.1%/79.4%; IIB = 71.4%/70.6%; IIC = 56.8%/55.7%; IIIA = 56.8%/69.4%; IIIB = 42.6%/56.8%; IIIC = 20.0%/33.3% and IIID = none/6.5%. Conclusion: The results show that new staging system could efficiently classify our Japanese melanoma cohort. Although there was no difference in Stage I and II disease between the 7th and 8th Edition systems, we should be careful in managing Stage III disease since the survival curves of the 8th Edition staging were completely different from the 7th Edition. Moreover, our results indicate that adjuvant therapies for Stage IIB and IIC should be developed, since the relapse-free survival for these stages were equivalent to Stage IIIA and IIIB, respectively.