A　novel　3D　porous　reduced　graphene　oxide/montmorillonite　composite　hydrogel　(rGO–MMT)　was　prepared　by　solvent　method,　where　the　MMT　nanosheets　were　homogenously　dispersed　in　3D　rGO　hydrogel.　The　porous　3D　structure　and　the　high　dispersion　of　MMT　nanosheets　can　promote　the　adsorption　capacity.　The　effects　of　MMT　content　(wt%),　the　initial　concentration　of　Cr(VI)　solution　(C0),　pH　value　(pH0),　the　adsorption　dose　and　temperatures　on　the　adsorption　capacity　of　rGO–MMT　for　Cr(VI)　ions　have　been　investigated.　The　optimum　pH　value　for　Cr(VI)　adsorption　is　2,　and　the　adsorption　capacity　increases　with　MMT　content　and　adsorption　temperature.　The　rGO–MMT　composite　hydrogel　displays　the　excellent　adsorption　property　for　both　the　heavy　metal　and　organic　pollutants.　The　adsorption　capacity　of　rGO–MMT　composite　hydrogel　is　obviously　higher　than　those　of　single　rGO　hydrogel　and　MMT　due　to　the　synergistic　adsorption　of　rGO　hydrogel　and　MMT.　The　adsorption　of　Cr(VI)　ions　on　the　rGO–MMT　composite　hydrogel　follows　linear　pseudo-second-order　kinetics,　and　the　Langmuir　model　describes　the　adsorption　process　much　better.　Thermodynamic　parameters　indicate　that　adsorption　is　spontaneous,　favorable　and　endothermic　in　nature.　Graphic　abstract:　[Figure　not　available:　see　fulltext.]　©　2020,　Springer　Nature　B.V.