Background: A fluoropyrimidine plus oxaliplatin is the standard of care for stage III colon cancer but a fluoropyrimidine alone is also recommended for stage III patients in Japanese and other practice guidelines. We assessed efficacy of adjuvant fluoropyrimidine with or without oxaliplatin across a population of stage III colon patients in the Multi-Institutional Registry of Large Bowel Cancer in Japan. Methods: 7,024 of stage III colorectal cancer patients in this registry were analyzed. Endpoints were relapse-free survival (RFS) and overall survival (OS). Results: All patients received adjuvant chemotherapy between 2008 and 2011.Patient characteristics except lymph node metastases were well balanced across groups. The RFS of fluoropyrimidine with or without oxaliplatin show comparable efficacy for stage III, even for stage IIIc patients, less than 70 years old, and T4 or N2b. Median follow-up was 74.9 months in oxaliplatin combined therapy and 74.7 months in fluoropyrimidine monotherapy. The additive efficacy of oxaliplatin was not shown for RFS and OS. Conclusions: Adjuvant fluoropyrimidine monotherapy and fluoropyrimidine plus oxaliplatin show comparable efficacy benefits for the treatment of stage III of Japanese colon cancer patients; supporting fluoropyrimidine alone as standard options for the adjuvant therapy of stage III in Japan.