Background <p>Multiple circRNAs are abnormally expressed in breast cancer (BC), which may be involved in tumor progression and promote anti-tumor drug resistance.</p> Aim <p>To explore the effect of hsa_circ_0062522 on the development of estrogen receptor-positive (ER+) breast cancer and tamoxifen (TAM) resistance.</p> Materials and methods <p>This study collected a total of 112 paired ER + breast cancer tumour tissues and adjacent tissues. The expression of hsa_circ_0062522 and miR-3163 in ER + breast cancer tissues and cells were determined by RT-qPCR. The cell viability, migration and apoptosis of MCF-7 and T-47D were determined by CCK-8, transwell and flow cytometry assays. Spearman correlation analysis and dual luciferase assay were perfprmed to verify the interaction between hsa_circ_0062522 and miR-3163. Establish a mouse model of xenograft with MCF-7 or T-47D cells to study the effect of hsa_circ_0062522 on ER + breast cancer in vivo.</p> Results <p>Hsa_circ_0062522 was increased, while miR-3163 was decreased in ER + breast cancer tissues and cells. Up-regulation of hsa_circ_0062522 promoted cell viability, cell migration and TAM resistance, but inhibited apoptosis in ER + breast cancer cells. Down-regulation of hsa_circ_0062522 had the opposite effect. Dual luciferase and cell function experiments confirmed that hsa_circ_0062522 affected the progression and TAM resistance of ER + breast cancer by regulating miR-3163. In vivo experiments have demonstrated that silencing hsa_circ_0062522 can reduce the volume and weight of tumors in mice and increase the sensitivity of tumors to TAM.</p> Conclusion <p>Hsa_circ_0062522 affects the activity, migration, apoptosis and TAM resistance of ER + breast cancer cells in vitro through miR-3163. In vivo, it influences the volume, weight and TAM sensitivity of tumors.</p>