Background: A combination of gemcitabine+erlotinib is one of the standard chemotherapies in advanced pancreatic cancer (APC). Since APC patients often take antiulcer drugs to prevent gastritis (e.g., NSAIDs to reduce cancer pain), erlotinib concentration is generally decreased through the mechanism of CYP3A4. Furthermore, unlike lung cancer, the biomarkers for APC are not obvious except rash. Here, we examined biomarkers of gemcitabine+erlotinib treatment in APC patients including the presence of antiulcer drugs. Methods: The subjects were 59 advanced pancreatic cancer patients. They were treated with gemcitabine+erlotinib starting from Nov. 2011 to Apr. 2013. Gemcitabine was administered at 1000 mg/m², on days 1, 8, and 15 for every 4 weeks, and erlotinib was taken 100 mg daily. The progression-free survival (PFS), UICC stage, sex, age, CRP concentration, performance status (PS), rash, and presence of antiulcer drugs were examined. The PFS curve was plotted according to the method of Kaplan and Meier. The difference in the PFS was calculated using the log-rank test, and a multivariate analysis was conducted using Cox hazard model. Results: UICC stages were as follows; i.e., stage II: 1, stage III: 8, and stage IV: 50. There were 36 males and 23 females, and their ages ranged from 41 to 82 years old (median: 65). The CRP concentrations ranged from 0.02 to 11.5 mg/dl (median: 0.57). 37 patients received antiulcer drugs, and 48 patients had rash. The univariate analysis revealed that the CRP concentration and rash were significant (p=0.009 and p=0.005, respectively). Low CRP (<0.57mg/dl) and presence of rash were related to good PFS. The multivariate analysis also revealed that the CRP concentration (HR, 0.34; 95%CI, 0.16-072; p=0.005) and rash (HR, 0.40; 95%CI, 0.16-0.96; p=0.04) were significant. The presence of antiulcer drugs on PFS was insignificant. Conclusions: The CRP concentration and rash were biomarkers of gemcitabine+erlotinib treatment in APC patients.