MicroRNAs　(miRs)　are　a　class　of　non-coding,　small　RNA　molecules　that　play　important　roles　in　gene　expression.　The　aberrant　expression　of　miRs　is　associated　with　various　human　diseases,　and　miRs　have　been　regarded　as　biomarkers　and　therapeutic　targets　in　cancer　treatment.　In　this　work,　using　miR-21　as　model　target　species,　an　efficiently　self-enhanced　rolling　circle　amplification　(seRCA)-based　biosensing　platform　was　developed　for　the　ultrasensitive　detection　of　cancer-related　miRs.　In　the　presence　of　target,　a　linear　DNA　template　can　be　cyclized　by　ligase　and　initiate　the　first　RCA　(fRCA)　reaction.　Without　any　separation　step　and　chemical　modification,　the　fRCA　products　(fRCAp)　are　capable　of　activating　the　second　exponential　RCA　and　produce　a　much　higher　fluorescence　signal,　causing　the　self-enhancement　effect　of　RCA　reaction.　Because　two　different　signal　amplification　processes　are　introduced,　there　are　two　linear　dynamic　ranges　together　over　7　orders　of　magnitude.　Target　miR　can　be　detected　down　to　1.0　fM　with　very　high　specificity,　eliminating　the　interference　from　homologous　miRs.　If　a　fluorescently　modified　oligonucleotide　probe　is　involved,　the　seRCA-based　biosensing　strategy　is　able　to　be　employed　for　the　intracellular　imaging　of　cancer-related　miR.　Significantly,　the　comparative　evaluation　demonstrates　that　the　proposed　strategy　exhibits　the　impressive　capability　to　execute　the　miR　imaging　within　cells　higher　than　classical　fluorescence　in　situ　hybridization　(FISH)　method.　The　newly-developed　powerful　sensing　strategy　for　the　specific　miR　imaging　would　offer　a　unique　opportunity　to　promote　molecular　biological　research,　early　diagnosis　and　treatment　of　human　cancers.