Synergism　is　an　important　strategy　to　enhance　the　bioavailability　of　pollutants　and　optimize　biotrickling　filter　(BTF)　performance.　The　synergistic　biodegradation　of　m-xylene　with　the　introduction　of　toluene　was　investigated　in　this　study.　The　packing　was　diatomaceous　earth　pellets　with　a　volume　of　2411　cm3.　The　empty　bed　residence　time　(EBRT)　of　the　BTF　was　kept　constant　at　25　s.　The　mixing　ratios　for　toluene　and　m-xylene　were　1:1,　1:2,　1:4,　and　1:6,　corresponding　to　the　inlet　loading　rate　(ILR)　of　m-xylene　from　about　36-216　g/m3/h,　and　the　toluene　ILR　was　maintained　at　about　36　g/m(3)/h.　The　biodegradation　performance　and　biofilm　characteristics　were　evaluated　under　these　various　mixture　compositions.　For　mixing　ratios　of　1:1,　1:2,　and　1:4,　m-xylene　was　synergistically　removed　with　toluene.　The　most　pronounced　synergism　occurred　when　the　ratio　was　1:2;　the　average　elimination　capacity　(EC)　of　m-xylene　increased　by　12.5%,　from　64　g/m(3)/h　to　72　g/m(3)/h.　The　presence　of　toluene　promoted　the　growth　of　microorganisms　and　improved　the　hydrophobicity　of　the　biofilm.　In　contrast,　for　the　1:6　toluene　and　m-xylene　mixture,　toluene　inhibited　the　degradation　of　m-xylene.　The　microbial　species　composition　analysis　revealed　that　Burkholderia　and　Mycobacterium　were　correlated　with　synergistic　removal　of　m-xylene,　especially　Burkholderia.