This study reports the adsorption of Cu(II) ion by 3-(2-aminoethylamino) propyldimethoxymethylsilane-modified terpolymers. Water-soluble poly(sodium 4-styrenesulfonate-co-maleic anhydride-co-acrylamide) [poly(NaSS-co-MA-co-AAm)] and poly(sodium 4-styrenesulfonate-co-maleic anhydride-co–N-isopropylacrylamide) [poly(NaSS-co-MA-co-NIPAM)] terpolymers were synthesized and then modified with silane to make them water-insoluble. 1H-NMR and FT-IR spectroscopy was used to study the chemical composition of the terpolymers. Also, acid number and viscosity of the polymers were determined. Cu(II) ion adsorption parameters (adsorbent dosage, contact time, pH and metal ion concentration) were studied, and the equilibrium data were evaluated using adsorption isotherm models; Freundlich isotherm gave the best fit. Cu(II) adsorption performance of poly(NaSS-co-MA-co-AAm) and poly(NaSS-co-MA-co-NIPAM) terpolymers was found to be 53.42 and 43.10%, respectively. The terpolymers can be used for removal of Cu(II) from aqueous media.