Oxaliplatin and oral fluoropyrimidines (capecitabine or S-1) are active agents for colorectal cancer. Recent a phase II trial of combination chemotherapy of oxaliplatin with S-1 (OS) and several phase II trial of combination chemotherapy of oxaliplatin with capecitabine (XELOX) demonstrated good activity and mild toxicity in advanced colorectal cancer. Oxaliplatin and S-1 or capecitabine have distinct mechanisms of action and no overlap of key toxicities. Furthermore, oxaliplatin and fluorouracil were shown to be highly synergistic, not only in preclinical models but also in subsequent clinical trials.