Gastric cancer (GC) remains a serious threat to human health with a high cancer-related death rate and unsatisfactory treatment effects after curative resection, especially with advanced GC. Thus, exploration of the molecular mechanism of cisplatin (CDDP) resistance in GC is crucial. circCCDC66 (hsa_-circ_0001313) expression was detected by quantitative reverse-transcription PCR in GC cell lines and tissues. The characteristics of circCCDC66 in CDDP resistance in GC were evaluated in vivo and vitro. We performed luciferin reporter assays, biotin-coupled RNA pull-downs and fluorescence in situ hybridization (FISH) to assess the relationship of miR-618 to circCCDC66. Function was determined by cytotoxicity assay, western immunoblotting and TUNEL. CircCCDC66 was overexpressed in CDDP-resistant cells and tissues. The circCCDC66 expression was significantly associated with malignancy and was an independent risk factor for disease-free survival (DFS) in GC patients treated by CDDP based chemotherapy. Data from in vitro and vivo experiments demonstrated that circCCDC66 inhibited apoptosis by targeting miR-618 and release of B-cell lymphoma-2 (BCL2). CircCCDC66 is an essential regulator in the development of CDDP resistance and may serve as a promising therapeutic target for GC patients. Otherwise, our study adds more evidence of circRNA functioning as a sequestering agent for miRNA. (C) 2020 Elsevier Inc. All rights reserved.