Here we report a case of metastatic colon cancer treated with 5-fluorouracil, leucovorin, and escalated doses of irinotecan (FOLFIRI) combined with regorafenib in the fourth-line setting after uridine diphosphate glucuronosyltransferase (UGT)1A1 genotyping analysis. A 66-year-old male was initially diagnosed with Union Internationale Contre le Cancer stage III descending colon cancer and underwent curative surgery. He received postoperative adjuvant chemotherapy; however, liver metastasis developed and a partial hepatectomy was performed thereafter. Unfortunately, pulmonary metastases and recurrent liver tumors were found despite a series of systemic treatments with multiple combinations of cytotoxic and biologic agents. Recently, a novel multikinase inhibitor, regorafenib, was approved for the treatment of metastatic colorectal cancer refractory to other therapeutic modalities. As further treatment, we combined regorafenib with FOLFIRI, which included dose escalations of irinotecan, after UGT1A1 genotyping analysis. The therapeutic results were promising, with the improvement in liver and pulmonary metastases being classified as stable disease and partial response, respectively. Moreover, the progression-free survival was over 6 months. FOLFIRI, with dose escalation of irinotecan according to UGT1A1 genotyping plus regorafenib appears to be a promising salvage therapy for patients with refractory metastatic colorectal cancer.