This　study　proposes　the　use　of　diatomaceous　earth　(DE)　as　a　surface-treating　agent　for　recycled　aggregate　(RA)　to　enhance　the　performance　of　recycled　aggregate　concrete　(RAC).　The　treatment　process　involves　pre-saturating　the　RA　and　applying　a　coating　using　a　slurry　composed　of　calcined　DE　and　ordinary　Portland　cement　at　specific　proportions.　Test　results　demonstrate　that　the　compressive　and　splitting　tensile　strengths　of　RAC　can　be　significantly　improved,　with　increases　of　up　to　20.0%　and　36.0%　respectively.　Additionally,　the　28-day　chloride　diffusion　coefficient　of　RAC　can　be　reduced　by　up　to　32.0%　by　adjusting　the　proportion　of　DE　in　the　slurry.　These　improvements　are　not　influenced　by　changes　in　the　quality　of　the　RA,　but　rather　by　the　enhanced　interfacial　transition　zone　(ITZ)　in　RAC.　Microscopic　measurements　of　the　ITZ　reveal　a　layered　structure　resulting　from　the　surface　treatment,　characterized　by　lower　porosity　and　higher　microhardness　compared　to　the　reference　RAC.　This　enhanced　ITZ　is　primarily　responsible　for　the　improved　macro-scale　performance　of　RAC.　The　findings　of　this　study　confirm　the　feasibility　of　using　DE　as　a　surface-treating　agent　for　RA　to　produce　RAC　with　enhanced　strength　and　durability.　Furthermore,　it　suggests　the　promising　use　of　DE　in　the　construction　industry,　avoiding　the　drawbacks　associated　with　using　high-dosage　DE　that　can　impact　concrete　consistency　and　water　demand.　©　2023,　The　Author(s),　under　exclusive　licence　to　RILEM.