Conjugated　microporous　poly(aniline)s　(CMPAs)　are　an　intriguing　material　platform　for　the　selective　capture　of　toxic　heavy　metal　ions　from　water.　However,　the　hydrophobic,　monotonous　N　heteroatom　and　microporous　properties　limit　their　application　scopes,　particularly　for　the　in-depth　treatment　requiring　to　a　parts　per　billion　(ppb)　level.　Herein,　we　report　a　novel　chitosan-anchored　CMPA　(CMPA-CS),　as　designed　through　delicately　exploiting　the　chitosan　as　either　adsorption　sites　or　pore　templates　for　CMPA　to　acquire　highly　functionalized　mesopores　that　could　considerably　facilitate　Hg(II)　adsorption.　The　CMPA-CS　thus　displayed　excellently　wide　pH　suitability　(1.0–13.0),　large　capacity　(862.1　mg　g−1),　ultrafast　removal　rate　(k2　=　0.163　mg　g−1　min−1),　high　affinity　(Kd　=　7.1　×　106),　and　strong　anti-interference　performance　(selectivity　of　minimum　94.5%　under　the　extreme　influence　of　100-fold-concentration　cations).　Besides,　the　Hg(II)　concentration　could　be　decreased　from　0.578　ppm　to　less　than　1.106　ppb　in　Minjiang　river　water　substrates,　below　the　EPR　drinking　water　standards　of　2　ppb.　Comprehensive　characterization　revealed　that　the　removal　mechanism　of　Hg　(II)　was　primarily　a　synergetic　chelation　reaction　from　the　unique　nitrogen　ligands　and　O-containing　groups,　with　the　following　features　intensified:　(i)　good　wettability　to　increase　the　interaction　between　CMPA　and　Hg(II)　as　contributed　by　the　plentiful　oxygen-containing　groups;　(ii)　hierarchical　mesopores　that　would　promote　ions　transport　efficiency　as　created　by　the　chitosan.　The　new　insight　in　this　work　can　offer　valuable　guidelines　for　the　design　and　structure　optimization　of　CMPAs,　facilitating　its　real-world　commercial　implementation.　©　2023　Elsevier　B.V.