BackgroundGastric cancer (GC) is the third most common cause of cancer-related death worldwide. Increasing studies have indicated that circular RNAs (circRNAs) play critical roles in cancer progression. However, the precise mechanism and functions of most circRNAs are still unknown in gastric cancer.MethodsIn the present study, we aim to uncover the mechanism by which circRNAs regulate gastric cancer tumorigenesis. By analyzing the microarray data, we screened differential expressed circRNAs in the gastric cancer group and identified a down-regulated circRNA, hsa_circ_0040039 (circSNTB2). Mechanically, circSNTB2 served as a sponge for the miR-6938-5p and up-regulated its expression.ResultsMeanwhile, G0/G1 switch gene 2 (G0S2) and programmed cell death gene 4 (PDCD4) were identified to be the aim genes of miR-6938-5p, constructing circSNTB2/miR-6938-5p/G0S2 and PDCD4 pathways.ConclusionTaken together, our findings demonstrated that circSNTB2 plays an essential role in gastric cancer by regulating miR-6938-5p through G0S2 and PDCD4 genes. CircSNTB2 could be a promising biomarker for GC diagnosis and targeted therapy.