There are limited absolute biomarkers for determining the prognosis before first- and second-line palliative chemotherapy in unresectable pancreatic cancer (urPC) patients. To find the best prognostic inflammatory marker, we investigated relationships between overall survival (OS) and six inflammatory markers; C-reactive protein/albumin ratio (CAR), neutrophil–lymphocyte ratio (NLR), prognostic nutrition index (PNI), platelet–lymphocyte ratio (PLR), Glasgow prognostic score (GPS), and prognostic index (PI). We examined 255 patients who received gemcitabine + nab-paclitaxel or FOLFIRINOX as first-line chemotherapy and 159 patients who subsequently underwent second-line chemotherapy. First-line patients with lower CAR had better OS compared to those with a higher CAR (hazard ratio 0.57; 95% confidential index 0.42–77;P< 0.01). Similarly, lower NLR (P= 0.01), higher PNI (P= 0.04), lower PLR (P= 0.03), GPS score of 0 (P< 0.01) and PI score of 0 (P< 0.01) were all associated with better OS. CAR demonstrated the best superiority for determining survival prognosis through the use of area under the curve of time-dependent receiver-operating characteristic curves. Furthermore, a lower CAR before second-line therapy exhibited better OS versus higher CAR (P< 0.01). Therefore, CAR might be a useful biomarker for predicting urPC patient prognosis in both first- and second-line chemotherapy.