DNA　as　a　programmable　molecule　shows　great　potential　in　a　wide　variety　of　applications,　with　the　dynamic　DNA　nanodevices　such　as　DNA　motors　and　walkers　holding　the　most　promise　in　controlled　functions　for　biosensing　and　nanomedicine.　However,　a　motor　or　walker　that　consists　of　DNA　exclusively　has　not　been　shown　to　function　within　cells　because　of　its　susceptibility　to　endogenous　nuclease-mediated　degradation.　In　this　contribution,　we　demonstrate　a　Y-shaped　backbone-rigidified　triangular　DNA　scaffold　(YTDS)-directed　DNAzyme　walker　that　functions　inside　living　cells　to　detect　microRNAs　(miRNAs)　with　high　sensitivity.　A　novel　Y-shaped　backbone　offers　access　to　geometrically　well-defined　configurations　and　increases　the　rigidity　of　DNA　assemblies,　providing　a　unique,　circular,　and　rigid　DNA　track　within　living　cells　without　non-nucleic　acid　auxiliary　materials　and　enabling　the　stepwise　movement　of　DNAzyme　in　an　inchworm　fashion.　This　strategy　is　extended　to　the　construction　of　larger　rigid　planar　geometric　polygon-based　DNA　walkers,　demonstrating　unprecedented　opportunities　to　build　dynamic　DNA　nanostructures　with　precise　geometry　and　versatile　functionality.　Copyright　©　2019　American　Chemical　Society.