Background: The serum tumor-marker in monitoring response to chemotherapy is not valid in advanced pancreatic cancer (PC). S100 calcium-binding protein P (S100P) has been reported as a predictive diagnostic index for PC and may serve as an early marker to activity of chemotherapy. The aim of this study was to analyze the correlation between the efficacies of chemotherapy and the kinetics of tumor-markers including serum S100P, carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9) in prospective cohort of advanced PC. Methods: Patients who were treatment naïve for advanced PC with liver mets were eligible. Serum levels of S100P, CEA, and CA19-9 were measured at baseline and at one month later. The patients without monitoring of tumor-markers were excluded. A response of tumor-marker was defined as a decrease of at least 25%. Clinical data including radiological response according to the Response Evaluation Criteria In Solid Tumors ver. 1.1 were prospectively collected. S100P, CEA, and CA19-9 responses were tested in association with progression free survival (PFS) and overall survival (OS). Results: Fifty patients were analyzed in this study (male: 64%, median age: 67 years, Eastern Cooperative Oncology Group performance status [PS] 0: 60%). All of 50 patients received chemotherapy (gemcitabine [GEM]: 13 pts, GEM doublets: 34 pts, 5FU-based regimen: 3 pts). PFS and OS were 2.8 and 6.1 months. Responses of S100P, CEA, and CA19-9 were founded in 50%, 16%, and 32% of all, respectively. Multivariate analysis for PFS in Cox regression hazard model was performed using age, gender, PS, CEA, CA19-9, and S100P, and revealed that the independent predictors to longer PFS were responses of S100P (HR to progression: 0.47, P=0.02) and CEA (HR: 0.29, P=0.01). S100P or CEA responders showed better OS in univariate analysis using log-rank test, compared to non-responders of S100P (responder vs. non-responder: 8.4 vs. 3.7 months, P=0.04) or CEA (12.0 vs. 5.9 months, P=0.02), but not in multivariate analysis. Conclusions: Biochemical response of S100P might be useful for monitoring response to chemotherapy in advanced PC, which warranted further study in relationship between serum S100P response and treatment efficacies.