Abstract: Circular RNA (circRNA) is a new type of non-coding RNA, which can form a closed covalent ring structure. More and more evidences have shown that circRNA is high conserved in evolution, ubiquitous in the genome of various eukaryotic cells and has a stable expression in the cytoplasm. CircRNA has many potential functions, such as being a miRNA sponge, or regulating gene transcription by binding to RNA related proteins to form an RNA protein complex. The findings of circRNAs in tumor suggest that circRNA may play an important role in the occurrence and development of tumor. Therefore, circRNA could be a new potential biomarker in the diagnosis and treatment of tumor.