Circular RNAs (circRNAs) have good stability and long half-life in blood and other body fluid,and possess regulatory effects on various biological processes as miRNA/RNA-binding protein sponges,or by competing endogenous RNA,indicating their great potential as biomarkers or targets of cancer therapy.In this study,we mainly explored the role and mechanism of circular RNA SMARCA5 (circsSMARCA5) in non-small cell lung cancer (NSCLC).Quantitative RT-PCR was applied to measure the expression levels of genes,and then,the relationships among circsSMARCA5,microRNA-670-5p (miR-670-5p),and RBM24 were further analyzed.Animal and cell experiments were performed to explore the functions of circsSMARCA5 in NSCLC cells.The results showed that circsSMARCA5 was expressed at low level in NSCLC tissues and cells,while miR-670-5p had high level in NSCLC tissues.Dual luciferase reporter assay verified that miR-670-5p was the target of circsSMARCA5,and RBM24 has the binding site of miR-670-5p.Further analysis showed that circsSMARCA5 could negatively regulate miR-670-5p and had positive relationship with RBM24.Moreover,circsSMARCA5 obviously inhibited tumor growth in vivo,reduced cell proliferation and increased cell apoptosis in vitro,while miR-670-5p mimic or RBM24 knockdown could reverse these effects.Thus,circsSMARCA5 may serve as an NSCLC suppressor by regulating the miR-670-5p/RBM24 axis,and it may have the potential to be a biomarker or therapeutic target for NSCLC.