The aim of this study was to investigate how preoperative chemotherapy affected the serum zinc concentrations in patients with pancreatic cancer (PC). Two hundreds and thirty-one patients with PC who underwent pancreatectomy at our department from 2013 to 2019 were enrolled in this study and measured for the serum zinc concentrations before pancreatectomy. Patient characteristics, course of treatment, and laboratory data were analyzed. One hundred thirty-five patients underwent upfront pancreatectomy and 58 received preoperative Gemcitabine + S1 (GEM + S1) and 29 received Gemcitabine + nab-Paclitaxel (GEM + nab-PTX). Comparing the serum zinc concentrations before and after preoperative treatment, it was found to decrease after treatment with statistical difference (79.3 μg/dl vs. 68.7 μg/dl, p < 0.001). The result was consistent with the investigation for both the patients who received GEM + S1 and those who received GEM + nab-PTX (p = 0.019, p < 0.001, respectively). The preoperative chemotherapy consistently reduced the serum zinc concentrations in the PC patients, regardless of their regimen such as GEM + S1 and GEM + nab-PTX. Monitoring the serum zinc concentration and appropriate zinc supplementation may be essential for PC patients undergoing preoperative chemotherapy and pancreatectomy.