Layered　composite　rocks　(LCRs)　are　often　encountered　in　underground　excavation　in　which　extensive　deformation,　buckling　and　local　collapse　near　the　layer　interface　frequently　occur.　However,　there　is　limited　advance　knowledge　of　the　failure　mechanisms　of　LCRs　to　interpret　the　field　observations　due　to　the　relative　scarcity　of　polyaxial　compression　testing.　To　that　end,　this　study　conducts　the　true-triaxial　experiments　with　the　acoustic　emission　(AE)　monitoring　on　the　LCR　specimens,　with　the　emphases　being　on　the　effects　of　mechanical　contrast　(MC)　between　the　layers　on　the　fracture　behaviors　under　true-triaxial　stresses.　First,　the　strength　of　LCRs　is　controlled　by　the　weaker　layer.　Second,　at　the　unstable　fracturing　phase,　high　AE　event　rate　is　faithfully　recorded　but　intermittently　interrupted　by　macrofracturing　in　granite　but　not　in　sandstone.　Third,　main　failure　planes　of　LCRs　appear　sub-orthogonally　to　σ　3　(minimum　principal　stress),　taken　the　form　of　delamination　fracture　and　exhibited　the　mode　of　σ　3-transverse-symmetric　fracturing.　As　the　distance　from　the　unloaded　surface　increases,　the　fracturing　transitions　from　σ　3-transverse-symmetric　spalling　to　σ　3-transverse-symmetric　shearing.　Depending　on　the　MC,　both　the　fracture　propagation　through　the　interface　and　the　fracture　containment　within　sandstone　are　registered.　Moreover,　the　interface　effect　is　numerically　revealed　through　a　3D　finite-element　modeling.　This　study　gets　insights　into　the　failure　mechanisms　of　LCRs　with　a　changing　mechanical　property　in　individual　layers　under　true-triaxial　stresses.　©　2023,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　GmbH　Austria,　part　of　Springer　Nature.