Circular RNAs (circRNAs) represent a class of non-coding RNA widely spreading in eukaryotic cells, with the feathers of structural stability, high abundance, cell or tissue-specific expression and so on. They involve in the regulation gene expression by multiple acting mechanisms. For example, several circRNAs contain microRNAs (miRNAs) competition sites, acting as competing endogenous RNAs (ceRNAs) to sequester microRNAs and terminate their suppression of targets genes. Ever since 2013, circRNAs analysis has been a popular research in RNA fields. Recent studies show, circRNAs’ expression and action are related to the occurrence or progression of various diseases, development of biologic tissue and cell aging. Their different expression probably make them to be ideal biomarkers in disease diagnosis or identification tissue development. And the clarity of their mechanisms in diseases also make them to be with the potential of effective therapeutic targets. The construction of circRNA database, the development of prediction tools and the deeply studies of their mechanisms will give a more widely application foreground for circRNAs.