A　new　porous　magnetic　chitosan-polyethylenimine　(Fe3O4/CS-PEI)　polymer　composite　was　synthesized　by　crosslinking　chitosan　(CS)　with　polyethylenimine　(PEI)　in　the　present　of　FeCl3.6H(2)O　and　FeCl2.4H(2)O　in　alkaline　condition　and　applied　to　remove　congo　red　(CoR)　from　aqueous　solutions.　The　Fe3O4/CS-PEI　composite　was　characterized　by　SEM,　XRD,　TGA　and　FT-IR　analysis.　The　polymer　composite　owned　high　positive　charge,　large　surface　area,　multi-level　pore　distribution　and　magnetic　responsiveness.　The　porous　magnetic　Fe3O4/CS-PEI　composite　showed　ultrahigh　capacity　(1876　mg/g)　for　CoR　removal.　It　removed　over　99.3%　of　CoR　(100　mg/L)　when　the　dosage　was　over　1.4　g/L.　A　higher　temperature　was　benefit　to　CoR　removal.　The　Fe3O4/CS-PEI　composite　was　effective　for　CoR　removal　in　a　wide　pH　range　(3-13).　Kinetics　studies　suggested　that　the　adsorption　mechanism　of　CoR　followed　the　pseudo-second　model　and　it　was　also　affected　by　the　boundary　layer　diffusion.　The　adsorption　process　followed　the　Redlich　Peterson　isotherm　equation.　Thermodynamic　studies　also　demonstrated　that　this　adsorption　process　was　spontaneous,　favorable　and　endothermic.　The　activation　energy　(E-a)　of　the　adsorption　process　was　34.08　kJ/mol,　indicating　that　chemisorption　existed　in　the　process.　The　results　demonstrated　that　the　porous　magnetic　Fe3O4/CS-PEI　polymer　composite　is　a　promising　adsorbent　for　the　efficient　removal　of　dye　pollutants　from　aqueous　solution.　(C)　2017　Elsevier　B.V.　All　rights　reserved.