A　comparative　study　was　conducted　on　the　biomass　properties,　microbial　community　composition,　and　func-tional　genes　of　four　particle-size　groups　of　denitrifying　granular　sludge　(DGS)　(S1:　0.1　＜=　d　＜　0.5　mm;　S2:　0.5　＜=　d　＜　1.0　mm;　S3:　1.0　＜=　d　＜　1.5　mm;　S4:　d　＞=　1.5　mm).　The　results　showed　that　the　settling　velocity　and　wet　density　increased　with　an　increase　in　particle　size.　The　sludge　volume　index　and　water　content　were　negatively　corre-lated　with　the　particle　size.　The　production　of　extracellular　polymeric　substances　(EPS)　and　the　ratio　of　protein　to　polysaccharides　increased　initially　and　then　decreased　with　an　increase　in　the　particle　size.　S3　achieved　the　highest　EPS,　which　combined　with　Ca2+　ions,　resulting　in　the　highest　integrity　coefficient.　A　similar　convex　trend　was　observed　for　the　specific　denitrifying　activity.　Illumina　sequencing　and　quantitative　polymerase　chain　re-action　indicated　that　microbial　community　diversity　and　richness　increased　with　the　particle　size.　S3　had　the　largest　number　of　denitrifying　genes.　Statistical　analysis　revealed　that　Aquimonas　and　Pannonibacter,　potential　hosts　of　the　narG/nirS/nirK/norB/nosZ　genes　and　narG/nirS/nirK/nosZ　genes,　respectively,　were　crucial　for　ni-trate　removal　in　the　larger-sized　DGS　(d　＞=　1.0　mm),　whereas　Lentimicrobium,　a　possible　host　of　the　napA　gene,　was　primarily　responsible　for　denitrification　in　the　smaller-sized　groups　(d　＜　1.0　mm).　These　results　indicated　that　DGS　with　a　particle　size　of　1.0-1.5　mm　had　superior　granular　structural　stability　and　denitrification　ca-pacity.　This　study　provides　a　new　perspective　for　cultivating　DGS　and　enhancing　its　denitrification　capacity　and　stability.