Phase I study of combination therapy with peptide vaccine and anti-cancer drug for colorectal cancer has been performed in our hospital. The purpose of this study was to evaluate the safety and immune response of different dose of RNF43-721 emulsified with Montanide ISA 51 in combination with S-1/CPT-11 chemotherapy. The study design was a dose escalation of peptide (0.5, 1.0, 3.0 mg) with three patients' cohort. Nine patients were enrolled. All patients were treated with peptide subcutaneously every week and two courses with S-1/CPT-11 chemotherapy. Vaccinations were well tolerated without any major adverse events. Immunological reactions are not analyzed yet. We herein report a case who has been evaluated to be long SD with this intervention for para-aortic LN metastasis from sigmoid colon cancer.