Background: For liver limited metastatic colorectal cancers, complete resection of liver metastases is the only potentially curative treatment and can significantly improve overall survival. The current goal of medical treatment for colorectal cancer with initially unresectable liver metastases is to maximize the rate of secondary resection. This phase II study is to explore whether FOLFOXIRI plus bevacizumab compared with FOLFOXIRI alone as first-line treatment could improve radical resectability in patients with RAS mutaion-type, unresectable liver-only metastatic colorectal cancer. Methods: The primary endpoint is the conversion rate of liver metastases, which is defined as the proportion of patients who had a curative liver treatment following protocol treatment, i.e., liver metastases that can be radical resected with or without ablation with no postoperative evidence of residual malignant disease. Secondary endpoints include safety, objective response rate, overall survival, progression free survival, quality of life and an assessment of predictive molecular markers of response. 160 cases of patients meet inclusion criteria and are enrolled in the trial will be randomized to two therapy groups: experimental arm A (FOLFOXIRI plus bevacizumab) or control arm B (FOLFOXIRI alone) in a 1:1 allocation ratio, stratifying for centers, ECOG status, synchronous or metachronous metastases, and a risk score derived from Nordlinger. All patients will receive the study treatment regimen every 2 weeks, and a total of the maximum of 12 cycles. CT scan or MRI of the abdomen will be performed after 2 or 3 cycles of therapy to assess clinical response and resectability of liver metastases by multidisciplinary team including hepatic surgeon. If liver metastases are not deemed to be resectable at this assessment, but tumor assessment demonstrates stable disease or partial response, therapy will continue with re-assessment for clinical response and resectability after the next cycle. Clinical trial information: NCT02350530