Chitosan grafted crotonaldehyde (CGC) by nucleophilic addition reaction of the amine group with α,β-unsaturated aldehyde was achieved by simple method using Lewis acid FeCl3.6H2O or ZrOCl2.8H2O as a catalyst. The product has been extensively characterized using FTIR, TGA, SEM, and EDX. The CGC was used for removal of hexavalent chromium from its aqueous solution. Batch experiment was tested using different contact times and initial Cr6+ ion concentrations under acidic condition (pH 1.5). Isotherm studies were achieved using variable models (Langmuir, Freundlich, and Tempkin) which showed a 10-fold greater uptake (434.78 mg/g) for modified chitosan over non-modified chitosan. The kinetics of Cr6+ adsorption by CGC followed the pseudo-second order model. This study proved that the CGC is a promising material for the treatment of wastewater containing Cr6+ ions.