The　concept　of　global　size　effect　theory　from　material　level　to　structural　level　is　raised.　The　material　level　is　described　by　a　Universal　Morphological　Model　(UMM)　that　accounts　for　the　size　effect　behaviors　introduced　by　the　mixture　variables　of　concrete,　whereas　the　structural　level　is　linked　to　the　size　effect　theory　based　on　quasi-brittle　fracture　mechanics.　First,　the　UMM　that　is　eligible　for　the　description　of　material-level　size　effect　is　established　and　verified.　Parametric　study　on　the　UMM　shows　that　the　mechanical　properties　of　concrete　are　insensitive　to　the　maximum　aggregate　size　(MAS)　at　a　critical　interface　crack　index　eta(c).　Secondly,　by　introducing　the　UMM　into　the　formulation　of　structural-level　size　effect,　a　global　size　effect　model　(GSEM)　expressed　as　a　variant　for　the　Type-2　size　effect　model　(SEM)　is　proposed.　Parametric　study　on　the　GSEM　shows　that　the　properties　and　the　scales　of　mesostructures　have　significant　influences　on　the　size　effect　behaviors　of　concrete　at　the　structural　level.　The　critical　interface　crack　index　eta(c)　determined　by　the　UMM　should　receive　sufficient　attention　in　large-scale　structural　concrete　design　in　practice.