The current chemotherapy for metastatic colon cancer has improved an overall survival. In this study, we retrospectively analyzed the efficacy of mFOLFOX6 in colorectal cancer patients with synchronous unresectable liver metastases and compared the prognosis between before and after the administration of mFOLFOX6. The subject was 28 patients of colorectal cancer with synchronous unresectable liver metastasis who received mFOLFOX6 as a first-line treatment from 2005 to 2010. The median frequency of mFOLFOX6 was 10 times( range, 2-24 times), relative dose intensity of oxaliplatin was 75.0% (range, 42 .9-100), response rate was 32%, and median progression-free survival was 9 . 9 months. Surgical resection of colorectal liver metastases was performed to 4 patients (14.3%) as a conversion therapy. The overall survival of the patients with mFOLFOX6 was significantly better than that of 31 patients who received the chemotherapy via hepatic artery or the chemotherapy before the administration of oxaliplatin (31.8 months vs. 15 .1 months, p<0.01). Our results suggested that mFOLFOX6 treatment for unresectable liver metastases of colorectal cancer was made not only the conversion therapy possible, but it has improved the prognosis when compared with previous treatment without oxaliplatin.