Background: Although many studies have identified several inflammation-based and/or nutritional markers with prognostic value for patients with various types of cancer, the optimal markers and cutoff values for these markers remain obscure. Therefore, this retrospective study aimed to identify optimal markers and their cutoffs. Methods: We compared prognostic values among established preoperative inflammation-based and/or nutritional markers in 225 patients who underwent R0 resection for stage III gastric cancer. Inflammationbased and/or nutritional markers comprised C-reactive protein to albumin ratio (CAR), neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), prognostic nutritional index (PNI), Glasgow prognostic score (GPS), and prognostic index (PI). Time-dependent receiver operating characteristic curves were analyzed to assess predictive ability and to determine the optimal cutoff values. Prognostic factors predicting overall survival (OS) and cancer specific survival (CSS) were analyzed using Cox proportional hazards models. Results: Multivariate analyses revealed that CAR and PLR cutoff values of 0.47 and 172, respectively, were independent prognostic factors for overall survival (OS) (HR, 2.257; 95% CI, 1.180-4.319; p = 0.014 and HR, 1.478; 95% CI, 1.025-2.133; p = 0.037, respectively) and cancer-specific survival (CSS) (HR, 2.771; 95% CI, 1.398-5.493; p = 0.004 and HR, 1.552; 95% CI, 1.029-2.341; p = 0.036, respectively). These results were different from those we previously reported in patients with stage II. Conclusions: Among inflammation-based and/or nutritional markers, CAR and PLR were independent prognostic factors of OS and CSS in patients with stage III gastric cancer. The optimal markers and their cutoff values should be determined in specific populations.