Perovskite　La2/3-xLi3xTiO3　is　a　typical　solid-state　electrolyte　for　all-solid-state　lithium-ion　batteries.　The　material　system　has　been　intensively　studied　because　of　its　high　bulk　ionic　conductivity　and　great　efforts　have　been　devoted　to　explore　the　structure-property　relationship　and　further　enhancement　of　the　property　through　structural　modification.　However,　the　microstructure　and　its　critical　role　in　the　ionic　conductivity　of　La2/3-xLi3xTiO3　remain　scarce　in　the　literature.　In　this　work,　based　on　an　in-depth　study　via　aberration-corrected　scanning　transmission　electron　microscopy　and　first-principles　calculation,　we　report　the　formation　of　intrinsic　layered　defects　which　act　as　Li-ion-blocking　layers.　By　forming　enclosed　loops　scaled　from　nanometers　to　micrometers,　the　layered　defects　are　found　to　occur　uniformly　at　domain　boundaries.　The　results　provide　insights　into　the　influence　of　these　layered　defects　on　Li-ion　transport,　as　well　as　their　formation　mechanism　as　a　result　of　phase　transition　at　high　sintering　temperatures,　paving　the　way　to　develop　novel　perovskite　solid-state　electrolytes　via　microstructure　engineering.　(C)　2021　Elsevier　Ltd.　All　rights　reserved.