A superb adsorbent for Cr(VI) removal with a high adsorption capacity and acidic resistance was facilely synthesized via in situ hydrothermal cross-linking and reduction reaction of poly-Schiff base using m-phenylenediamine and glutaraldehyde as feedstock. The hydrothermal process effectively facilitated the condensation between aldehyde and amine group to strengthen the chemical structure by cross-linking the polymeric chains. Morphological evolution of the polymer via disaggregation and reassembly to finally form regular core-shell configuration was observed. The produced nanoparticles possess the excellent adsorption performance (833.3 mg g(-1)), far beyond most of the reported adsorbents, and exhibit fine reusability. The possible adsorption mechanism can be attributed to Cr(VI) electrostatic adsorption followed by redox reaction and chelation.