Using gamma radiation, a chitosan-poly (acrylamide-co-maleic acid) hydrogel was created by copolymerizing acrylamide and maleic acid onto the surface of chitosan. The shape, thermal stability, and structure of the hydrogel were confirmed by Fourier transform infrared analysis, scanning electron microscopy, thermogravimetric analysis, and differential thermal analysis. The batch adsorption of Eu(III) ions from an aqueous solution showed a rapid initial uptake with an equilibrium time of 24 h at pH (∼4). The Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models were used to study the adsorption equilibrium data. The adsorption behavior of Eu(III) ions closely followed the Langmuir isotherm, exhibiting a maximum adsorption capacity of 144.96 mg/g. The adsorption kinetics of Eu(III) ions are best described by the pseudo-second order model. The thermodynamic parameters were studied and revealed that the adsorption process was spontaneous, exothermic, and favorable at a lower temperature. 0.1 M HCl and AlCl desorbed Eu(III) ions with 97.09% and 88.63%, respectively. Hence, the hydrogel will serve as a starting point for the adsorption of trivalent lanthanide ions in the future.