Inorgano–organo–bentonite　(PMBt)　was　synthesized　through　co-modification　of　bentonite　with　manganese　oxides　and　poly(dimethyldiallylammonium　chloride)　(PDMDAAC),　and　was　utilized　to　remove　low-concentration　arsenic　from　water.　The　hybrid　material　was　characterized　by　means　of　X-ray　powder　diffraction　(XRD),　scanning　electron　microscopy　(SEM)　and　N2　adsorption–desorption.　It　was　revealed　that　the　hybrid　material　possessed　an　amorphous　structure　and　displayed　uneven　manganese　oxides　particles　gathering　about　the　bentonite　aggregates　with　a　large　BET　area　of　128.90　m2/g.　The　effects　of　adsorption　parameters　were　investigated,　such　as　stirring　time,　arsenic　concentrations,　adsorbent　dose,　temperature,　pH,　added　anions　and　ionic　strength.　The　adsorption　kinetics　and　equilibrium　of　arsenic　on　the　co-modified　bentonite　were　further　determined.　The　results　revealed　that　the　adsorption　of　arsenic　was　dramatically　affected　with　change　in　solution　pH　and　significantly　suppressed　by　phosphate　anion.　The　adsorption　kinetic　data　was　best　fitted　with　the　linear　pseudo–second–order　model　and　was　well　with　the　non-linear　Bangham　model.　The　equilibrium　data　were　well　simulated　with　the　Brunauer–Emmett–Teller,　Freundlich　and　Redlich–Peterson　isotherms　by　either　non-linear　or　linear　regression,　respectively.　The　non-linear　Langmuir　isotherm　showed　best　fitting　and　the　maximal　adsorption　capacity　was　9.14–9.99　mg/g,　dependent　on　the　error　function　used.　It　was　suggested　that　the　hybrid　material　had　a　heterogeneous　surface　and　high　affinity　towards　arsenic,　which　is　highly　favorable　for　arsenic　adsorption　following　a　non-ideal　monolayer　adsorption　model.　Based　on　the　above　comprehensive　analysis,　the　plausible　mechanism　for　arsenic　adsorption　on　PMBt　was　suggested　as　a　mixed　removal　mechanism　i.e.,　electrostatic　attraction　followed　by　inner-sphere　complexation.　©　2017　Elsevier　Ltd