Background: The combination regimen of TAS-102 and bevacizumab as salvage-line therapy for metastatic colorectal cancer (mCRC) was established based on its high clinical effectiveness (C-TASK FORCE). Recently, our current phase II TAS-CC3 study demonstrated comparable median progression-free survival (PFS: 4.5m) and overall survival (OS: 9.2m) with exclusive inclusion of 3^rd line therapy patients. However, practical predictors for its efficacy are lacking. This study evaluated inflammation-based scores as potential predictors for this combination therapy. Methods: This is a post hoc analysis of investigator-initiated, open-label, single-arm, multicentered phase II study (TAS-CC3) in Japan with 32 mCRC patients treated with the combination therapy. We investigated the predictive and prognostic values of pretreatment blood inflammation-based scores, including neutrophil-to-lymphocyte (NLR), platelet-to-lymphocyte (PLR), and lymphocyte-monocyte ratios (LMR), on disease-control (DC), PFS and OS. These were divided into two groups (high and low) using cut-off of each median values. This study was registered at the University Hospital Medical Information Network, as UMIN#000022438. Results: ROC curve analyses of 3 inflammation-based scores versus DC showed a best predictive performance in LMR, followed by NLR and PLR (AUC: 0.89, 0.85, and 0.68, respectively). The high LMR group had a significantly higher DC rate than the low group (87.5 vs. 43.8%, P= 0.023). Two patients showing partial responses were in the high group. The high LMR group showed significantly longer survivals compared with the low group (4.9 vs. 2.3m, respectively for median PFS, P= 0.014) (20.5 vs. 5.1m, respectively for median OS, P< 0.001). The values of LMR were significantly correlated with PFS and OS (r = 0.56: P< 0.001 and 0.62: P< 0.001, respectively). Conclusions: Pretreatment LMR is a valid predictive and prognostic biomarker for mCRC patients with TAS-102 and bevacizumab treatment and might be clinically useful for selecting patients of the responder. Clinical trial information: 000022438.