Ferroptosis is a form of regulated cell death driven by oxidative injury promoting lipid peroxidation, although detailed molecular regulators are largely unknown. Here, we show that heatshock 70-kDa protein 5 (HSPA5) negatively regulates ferroptosis in human pancreatic ductal adenocarcinoma (PDAC) cells. Mechanistically, activating transcription factor 4 (ATF4) resulted in the induction of HSPA5, which in turn bound glutathione peroxidase 4 (GPX4) and protected against GPX4 protein degradation and subsequent lipid peroxidation. Importantly, the HSPA5–GPX4 pathway mediated ferroptosis resistance, limiting the anticancer activity of gemcitabine. Genetic or pharmacologic inhibition of the HSPA5–GPX4 pathway enhanced gemcitabine sensitivity by disinhibiting ferroptosis in vitro and in both subcutaneous and orthotopic animal models of PDAC. Collectively, these findings identify a novel role of HSPA5 in ferroptosis and suggest a potential therapeutic strategy for overcoming gemcitabine resistance. Cancer Res; 77(8); 2064–77. ©2017 AACR.