A　sequencing　batch　reactor　operated　in　anoxic/aerobic　mode　was　used　to　investigate　the　effects　of　simultaneous　nitrogen　(N)　and　phosphorus　(P)　absence　in　activated　sludge.　Through　controlling　the　N　and　P　content　in　the　influent　water,　we　investigated　changes　in　sludge　concentration,　settling　performance,　morphological　structure,　surface　properties,　extracellular　polymer　content,　and　microbial　community　structure　and　function.　When　N　and　P　were　simultaneously　absent,　the　relative　hydrophobicity　of　the　activated　sludge　and　the　sludge　concentration　decreased.　The　specific　oxygen　uptake　rate　also　decreased,　the　activated　sludge　did　not　bulk,　and　the　flocs　were　larger　and　more　concentrated.　The　content　of　extracellular　polysaccharides　did　not　significantly　change.　An　increase　in　the　concentration　of　extracellular　proteins,　particularly　loose-binding　layer　proteins,　improved　activated　sludge　aggregation.　The　structure　and　function　of　the　activated　sludge　microbial　community　changed　significantly　in　the　absence　of　both　N　and　P,　with　a　significant　decrease　in　the　relative　abundance　of　species　related　to　N　and　P　metabolism.　Tax4Fun　analysis　showed　that　the　absence　of　both　N　and　P　decreased　metabolism　and　genetic　information　processing　of　the　microbial　community.　These　results　elucidate　the　effects　of　simultaneous　N　and　P　absence　on　activated　sludge　from　the　perspective　of　microbial　community　structure　and　function.　These　results　will　be　useful　for　treatment　of　N　and　P　deficient　wastewater　by　the　activated　sludge　method.