Abstract: Circular RNA (circRNA) is a type of endogenous single-stranded closed RNA with a stable structure, high conservation, and abundant expression in multiple species. Previous studies have indicated that circRNAs play roles in gene splicing, transcriptional regulation, and parental gene modification by acting as microRNA (miRNA) sponges. circRNAs are primarily synthesized via lariat-driven circularization, intron–pairing–driven circularization, and intron cyclization. The levels of some circRNAs are upregulated in gastric cancer (GC) tissues, and they function as oncogenes to promote the proliferation and migration of GC through the miRNA/p53/epithelial-mesenchymal transition axis and other mechanisms. However, the levels of other circRNAs are down regulated in GC tissues, and they inhibit the proliferation and migration of GC cells by acting as miRNA sponges. Many GC-related circRNAs have been identified in human saliva, gastric juice, and plasma, implying that circRNAs have great potential to be used as biomarkers of GC. Thus, circRNAs may act as a new target in the treatment of GC by intervention of circRNA expression to improve the sensitivity of anti-tumor drugs, synthesis of antioncogenic circRNAs, or down regulation of downstream signaling proteins of oncogenic circRNAs.