Oxaliplatin is a key drug for the treatment of metastatic colorectal cancer and 5-fluorouracil, leucovorin, and oxaliplatin (FOLFOX) is recognized as one of the standard regimen for first-line chemotherapy . Although both FOLFOX4 and FOLFOX6 have been used globally, FOLFOX4 involves two 22-hour FU infusions of fluorouracil (FU) every 2 weeks. The FOLFOX6 regimen has replaced FOLFOX4 in several countries, affording modestly greater convenience with one 2- day infusion. Though its introduction to Japan was delayed compared to other countries, oxaliplatin in combination with infusional 5-FU and l-leucovorin (l-LV) was approved in Japan in March 2005, with the oxaliplatin dose limited to 85 mg/m2 every 2 weeks. In Western countries, multiple regimens with a variety of oxaliplatin doses given every 2 or 3 weeks (FOLFOX4, FOLFOX6 and FOLFOX7), have been developed. Although FOLFOX4, modified FOLFOX6 with oxaliplatin at a dose of 85 mg/m2, and oxaliplatin monotherapy at a dose of 130 mg/m2 have shown good efficacy in Japanese patients, it remains unclear whether the efficacy and safety of FOLFOX6 with oxaliplatin at a dose of 100 mg/m2 would be similar to those in Western patients . Therefore, we conducted a phase II study of FOLFOX6 in Japanese patients with unresectable metastatic colorectal cancer to assess the efficacy and safety of FOLFOX6 with a dose of oxaliplatin of 100 mg/m2.