A novel microRNA (miRNA) quantification method has been developed using one-step rolling circle-quantitative PCR (RC-qPCR) analysis. Vent (exo-) DNA polymerase is firstly utilized to combine a rolling circle amplification (RCA) and qPCR in one step with high sensitivity and specificity in our RC-qPCR assay. Before performing the RC-qPCR, a padlock probe is ligated only when it is perfectly hybridized with miRNA. This ligation-based miRNA assay is highly specific for mature miRNAs, discriminating among related miRNAs that differ by as little as one nucleotide. It exhibits a dynamic range of seven orders of magnitude with a detection limit of 500 aM, and could be also used for the quantification of other small RNA molecules such as short interfering RNAs (siRNAs).