Colon cancer is a major health problem worldwide. While chemotherapy remains a main approach for treating late-stage colon cancer patients, most, if not all, of them will develop drug resistance and die of uncontrollable disease progression eventually. Therefore, identification of mechanism of drug resistance and development of overcoming strategy hold great significance in management of colon cancer. In this study, we discovered that activation of the PERK branch of the unfolded protein response (UPR) pathways is required for colon cancer cells to survive treatment of 5-Fluorouracil (5-FU), one of the first-line chemotherapeutics for late-stage colon cancer patients. Genetic and pharmacological inhibition of PERK or its downstream factors greatly sensitize colon cancer cells to 5-FU. Most importantly, in vivo use of PERK inhibitor synergizes with 5-FU in suppressing the growth of colon cancer cells in mouse models. In summary, our findings established a promising way to overcome resistance to chemotherapy in colon cancer.