Innovative techniques to measure microRNA (miRNA) in vivo could greatly improve the fundamental understanding of complex cellular processes. Herein, we report a novel method for real-time, quantitative miRNA detection inside living cells based on core-satellite plasmon rulers (PRs). This approach allows for the statistical analysis of single hybridization event caused by target miRNA. We investigated hundreds of satellite leaving events and found that the distribution of the time range for one strand displacement event is miRNA concentration-dependent, which obeyed Poisson statistics. Probing several such PRs under dark-field microscopy would provide precise determination of miRNA in vitro and in living cells, without photobleaching or blinking of the fluorophores. We believe the simple and practical approach on the basis of dynamic PRs with single-molecule sensitivity combined with statistical analysis hold promising potential to visualize native nucleic acids with short sequence and low-abundance.