In　this　work,　we　employed　target-driven　assembly　of　a　Mg2+-dependent　DNAzyme　to　develop　an　ultrasensitive　electrochemical　biosensor　for　the　simultaneous　detection　of　miRNA-21　and　miRNA-141.　The　target　miRNAs　could　hybridize　with　two　partial　DNAzymes,　facilitating　the　formation　of　a　stable　and　active　Mg2+-dependent　DNAzyme.　With　the　help　of　the　Mg2+　cofactor,　the　DNAzyme　could　circularly　cleave　the　ferrocene　(Fc)　or　methylene　blue　(MB)　labelled　hairpin　probes　and　release　Fc　and　MB　labels　from　the　electrode　surface,　which　could　significantly　amplify　the　current　suppression　to　achieve　multiple　detection　of　small　amounts　of　miRNA-21　and　miRNA-141.　This　electrochemical　biosensor　showed　high　sensitivity　and　selectivity　for　the　simultaneous　detection　of　miRNA-21　and　miRNA-141.　Furthermore,　the　proposed　method　was　also　successfully　applied　for　the　determination　of　miRNA-21　and　miRNA-141　from　diluted　serum　samples.　Overall,　the　proposed　sensor　showed　several　considerable　advantages　including　simple　preparation,　high　sensitivity,　and　enzyme-free　signal　amplification.　Therefore,　the　proposed　electrochemical　biosensor　could　be　used　as　a　highly　efficient　amplification　strategy　for　simultaneous　detection　of　various　miRNA　biomarkers　in　bioanalysis　and　clinical　diagnostics.