Abstract Gastric cancer is the most common gastrointestinal malignant tumor and also the second leading cause of cancer-related mortality worldwide. Given its high rate of non- symptoms at early stage, gastric cancer is usually diagnosed at middle or advanced stage with metastasis. Therefore, chemotherapy, including Cisplatin, becomes a main treatment option, in addition to surgery. However, it is not uncommon for patients to develop cisplatin resistance which limits its clinical applications. URI, a prefoldin family member and also an oncoprotein, has been shown to promote multiple cancer development, including gastric cancer. The aim of this study was to investigate how URI may participate in the DNA damage repair of gastric cancer cells induced by Cisplatin and its possible mechanism via the ATM/CHK2 pathway. URI knockdown cell lines from gastric cancer cells MGC-803 and SGC-7901 were established and treated with different concentrations of Cisplatin. Cell viability, proliferation and apoptosis were analyzed by CCK-8, EDU assay, and flow cytometry respectively. DNA injury marker H2AX were examined by qRT-PCR and Western blot analysis. Comet assay was used to detect the DNA damage. The results showed that URI knockdown reduces cell viability and proliferation, as well as the Cisplatin-induced apoptosis of gastric cancer cells. Cisplatin dose responsively induced DNA damage in gastric cancer cells and URI knockdown enhanced this damage as indicated by comet assay and increased γH2AX expression. We have also detected increased levels of P-ATM and P-CHK2 in gastric cancer cells treated with Cisplatin, while URI knockdown decreased the P-ATM and P-CHK2 expression after the cells were treated with cisplatin for 12 hours. Taken together, our results support that URI reduces DNA damage and promotes DNA repair of gastric cancer cells induced by cisplatin and therefore, enhances its resistance possibly via the ATM/CHK2 pathway Citation Format: Huiqin Bian, Yaojuan Lu, Yu Gu, Xiaojing Zhang, Lichun Sun, Junxia Gu, Qiping Zheng. URI participates in cisplatin-induced DNA damage repair of gastric cancer cells via the ATM/CHK2 pathway [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5914.