A　sensitive　and　homogeneous　electrochemical　aptasensor　was　fabricated　for　the　detection　of　mucin　1　(MUC1)　by　combining　a　well-designed　DNA　bulge-loop　(L-DNA)　structure　with　high-efficient　exonuclease　I　(Exo　I)-assisted　target　recycling　amplification　strategy.　The　L-DNA　probe　was　constructed　via　the　hybridization　of　the　MUC1　aptamer　and　methylene　blue　(MB)　labeled　complementary　DNA　(cDNA)　(cDNA-MB)　and　hence　could　not　diffuse　freely　to　the　negatively　charged　ITO　electrode　surface　due　to　the　strong　electrostatic　repulsion,　so　small　electrochemical　signal　was　detected.　The　addition　of　MUC1　caused　the　dissociation　of　L-DNA　structure　due　to　the　specificity　between　aptamer　and　MUC1.　Then　Exo　I　was　implemented　to　digest　the　released　cDNA-MB　into　mononucleotides　and　then　produced　short　MB-labeled　mononucleotides　fragments　(MB-MFs).　As　the　MB-MFs　contained　few　negative　charges,　it　diffused　easily　to　the　negatively　charged　ITO　electrode　surface　and　resulted　in　the　enhanced　electrochemical　signal.　Meanwhile,　the　MUC1-aptamer　complex　was　also　specifically　digested　by　Exo　I,　resulting　in　the　liberation　of　MUC1　and　hence　realized　the　target　recycling　and　then　caused　the　amplification　of　the　electrochemical　signal.　The　enhanced　electrochemical　signal　has　a　good　linear　relationship　with　logarithm　of　MUC1　concentration　in　the　range　of　1.0　pg　mL(-1)-50　ng　mL(-1)　with　a　limit　of　detection　of　0.40　pg　mL(-1)　(S/N　=　3).　Additionally,　the　fabricated　aptasensor　has　been　successfully　applied　to　detect　MUC1　in　serum　samples　with　satisfactory　results　and　thereby　it　exhibits　great　potential　in　the　practical　application　of　clinical　diagnosis.