Gastric cancer (GC) is a common malignancy and is the third leading cause of cancer-related death. At present, there is no simple and effective screening method for early-stage GC, and the treatment results and prognosis are poor. With the continuous improvement of molecular biology techniques, research on circular RNA (circRNA) has gradually expanded over time. Much data supports the role of circRNA in tumorigenesis. Moreover, due to its structural specificity and biological stability, circRNA is anticipated to be a potential biomarker for tumor diagnosis. Studies have confirmed that circRNA can participate in the proliferation, invasion, metastasis, and apoptosis of GC. These findings will lead to novel directions for the diagnosis and treatment of GC. This article reviews the structure and function of circRNA, summarizes the current studies on circRNA, and discusses the potential diagnostic value of circRNA in GC.