Abstract: Circular RNA （circRNA） as a newly discovered covalently closed circular noncoding RNA， is produced from back splicing and exists in a variety of biological cells， characterized by the stable structure， conserved sequence and some tissuespecificity. Recent studies show that circRNAs function as microRNA sponges to inhibit miRNA activity， involving the regulation of gene transcription and binding with RNAbinding proteins. As the new regulatory molecules， circRNAs play an important role in tumor development and progression， and serve as the novel potential biomarkers，providing new strategies for cancer diagnosis and targeted therapy. Herein， we review the properties， biogenesis， and functions of circRNAs and discuss its role in cancer.