Abstract: Circular RNA (circRNA) is a non-coding closed-loop single-stranded RNA molecule lacking the 5' end cap and the 3' poly (A) tail. Circular RNA is more abundant and stable than linear mRNA, and its expression is more conservative and specific. circRNA regulates cancer development through a variety of mechanisms, including miRNA sponges, regulating gene transcription, regulating RNA-binding proteins, and protein translation. This review summarizes the role of circRNA in cancer and helps to develop new clinical diagnostic techniques and treatments.