The　present　study　investigates　the　performance　of　recycled　aggregate　concrete　(RAC)　exposed　to　external　sodium　sulfate　(Na2SO4)　attacks　in　two　environments　(i.e.,　the　full-soaking　and　the　dry-wet　cycling　environments)　on　both　the　micro　and　macro　scales.　It　was　found　that　the　erosion　products　generated　in　RAC　were　indentical　to　those　in　NAC　in　both　environments,　but　sulfate　ions　accumulated　faster　in　RAC　than　in　NAC.　On　the　micro　scale,　the　old　ITZ(2)　presented　the　most　stabilized　performance　under　sulfate　attacks　compared　to　new　ITZ　(i.e.,　ITZ(1)　between　the　unwrapped　old　aggregate　and　the　new　mortar,　and　ITZ(3)　between　the　old　and　new　mortars);　the　old　mortar　degraded　more　drastically　than　that　of　the　new　mortar　after　long　exposure.　It　was　suggested　that　the　new　ITZ　and　the　old　mortar　should　be　the　primary　weak　phases　vulnerable　to　external　sulfate　attacks.　On　the　macro　scale,　the　mechanical　performance　of　RAC　(i.e.,　compressive　strength,　local　density　degree,　and　dynamic　modulus　of　elasticity)　first　increased　and　then　diminished　over　the　erosion　age　in　both　environments,　which　was　closely　related　to　the　property　changes　in　ITZ　and　mortar　on　the　micro　scale.　The　faster　performance　deterioration　of　RAC　after　long　exposure　indicates　the　inferior　resistance　of　RAC　to　external　sulfate　attakcs　in　comparisons　with　that　of　NAC.　The　dry-wet　cycles　can　enhance　the　sulfate-induced　damages　to　RAC　on　both　the　micro　and　macro　scales　when　compared　to　the　full-soaking　condition.　This　study　thereby　suggests　the　careful　structural　use　of　RAC　in　sulfate-rich　environments,　especially　where　sulfate　ingress　is　coupled　with　dry-wet　cycles.　(C)　2020　Elsevier　Ltd.　All　rights　reserved.