Conceptual　analysis　is　performed　to　examine　the　effects　of　pore　features　on　the　water　continuity　in　unsaturated　porous　systems.　The　roles　of　pore　features　in　relative　chloride　diffusion　coefficient　(D-rc)　of　mortar　specimens　at　various　degrees　of　water　saturation　(S-w)　were　studied　based　on　mercury　intrusion　porosimetry　and　resistivity　tests.　It　is　found　that　the　role　of　pore　structure　in　the　D-rc-S-w　relationship　is　a　result　of　its　effect　on　the　water　continuity.　Porosity　and　tortuosity　are　not　relevant　to　the　D-rc-S-w　relationship.　A　finer　pore　size　distribution　or　lower　pore　connectivity　tends　to　result　in　a　lower　D-rc.　The　pore　size　effect　on　the　D-rc　is　pronounced　primarily　at　high　S-w,　while　the　D-rc　is　dominated　by　the　pore　connectivity　at　low　S-w.　Cement　mortar　with　a　higher　water-to-binder　ratio　shows　larger　chloride　diffusion　at　high　relative　humidity　levels　but　smaller　chloride　diffusion　at　low　relative　humidity　levels.