Background: In the treatment for mCRC, it is essential for understanding the prognosis of each individual patient. Köhne’s index (KI) based on performance status, white blood cell count, alkaline phosphatase and number of metastatic sites has been previously proposed. However, in the salvage setting, the validity of KI has not been reported in patients treated by cetuximab-based chemotherapy. Methods: 269 patients with mCRC treated by cetuximab contained chemotherapy were retrospectively registered from 27 centers in Japan. This analysis was included in the KRAS wild-type patients who were refractory to or intolerant for 5-FU/irinotecan/oxaliplatin and were never administered anti-EGFR-antibody. Univariate and multivariate analysis for overall survival were performed using patient characteristics. Survival analyses were performed with Kaplan-Meier method, log-rank test and Cox proportional hazards model. The analysis was also designed to determine whether the Köhne’s classification could be extended to other endpoints such as progression-free survival. Results: All data were available for prognostic categorization in 127 patients. Median overall and progression-free survival was 9.8 and 4.2 months. The distribution and median survival / progression-free survival for KI were as follows: low risk (L) (n = 40; 13.1/5.1 months), intermediate risk (I) (n = 17; 9.6/3.5 months), and high risk (H) (n = 70; 7.6/4.1 months). For overall survival, there was significant difference between L and H (p = 0.004), but not between L and I (p = 0.213), and between I and H (p = 0.321). For progression-free survival, there was tended to difference between L and H (p = 0.083), but not between L and I (p = 0.392), and between I and H (p = 0.630). In Cox multivariate analysis, KI showed an independent prognostic impact (HR 1.370, p = 0.010), but not predictive impact (HR 1.147, p = 0.212). Conclusions: In this analysis, KI might be a prognostic factor in salvage treatment with cetuximab-based regimen, but no effect predicted impact. Moreover, the prospective evaluation is needed for the further validation.