Microstructure-property　relationship　has　drawn　strong　attention　in　modern　material　science.　The　progress　achieved　in　this　field　relies　on　a　common　basis　that　the　material　performance　originates　from　the　microstructure.　This　paper　brings　together　new　insights　and　facts　from　experiments　regarding　the　pore　size　dependent　connectivity　and　its　relation　to　ionic　transport　property　in　saturated　cementitious　materials.　An　innovative　measurement,　i.e.　intrusion-extrusion　cyclic　mercury　porosimetry　(IEC-MIP),　is　proposed　to　distinguish　between　the　small　capillary　pores　that　are　present　within　clusters　of　hydration　products　and　the　large　capillary　pores　that　are　left　out　of　hydration　products.　The　distribution　of　connectivity　as　a　function　of　pore　size　in　cementitious　materials　is　analyzed.　A　novel　transport　parameter,　i.e.　connectivity　of　small　capillary　pores,　is　introduced　and　quantified　by　IEC-MIP　measurements.　The　ionic　transport　was　measured　by　means　of　rapid　chloride　migration　tests.　A　power　relationship　is　established　between　connectivity　of　small　capillary　pores　and　chloride　migration　coefficient　for　cementitious　materials　irrespective　of　the　binder　type.　(C)　2019　Elsevier　Ltd.　All　rights　reserved.