A　comprehensive　study　from　detailed　microstructure　analyses　to　mass　transport　investigations　was　implemented　to　explore　chloride　penetration　of　unsaturated　alkali-activated　slag　(AAS)　mortars　accounting　for　chloride　binding　behaviors.　Unsaturated　chloride　penetrations　reflected　from　diffusion　cases　of　instantaneous　plane　source　and　sorption　cases　of　wetting-drying　exposure　were　elaborated　in　relation　to　solid　hydrates　and　pore　structure　features.　It　is　found　that　the　specimen　with　lower　saturation　has　a　slower　chloride　diffusion　but　a　larger　chloride　penetration　under　wetting-drying　cycles.　Slag　mortars　with　sodium　hydroxide　activation　exhibit　higher　chloride　binding　capacity　owing　to　more　hydrotalcite-like　phases　and　higher　Ca/Si　ratio　of　C-(N-)A-S-H　gels　in　the　outer　product　zones　as　compared　to　sodium　silicate　activated　slag　mortars,　regardless　of　the　saturation.　Accelerations　of　the　chloride　penetration　under　the　wetting-drying　exposure　are　limited　in　saturated　AAS　specimens　while　for　unsaturated　AAS　specimens　more　wetting-drying　cycles　result　in　the　inner　layers　to　be　gradually　diffusion-controlled.　The　chloride　binding　capacity　of　AAS　specimens　follows　Langmuir＇s　isotherm　and　clearly　decreases　with　a　lower　saturation.　It　is　advised　to　consider　the　electrical　double　layer　effect　within　narrow　pores　when　applying　rapid　chloride　migration　tests　for　AAS　systems.　©　2023　Elsevier　Ltd