In this work, three different generations of Poly(amidoamine) dendrimers (PAMAM) decorated on magnetic Fe₃O₄ composites (Fe₃O₄@SiO₂–G1, Fe₃O₄@SiO₂–G3, Fe₃O₄@SiO₂–G5) were fabricated and characterized by FTIR, XRD, TEM, TGA, VSM and XPS. The obtained composites were used for Cr(VI) removal. Batch adsorption studies showed that the adsorption reached equilibrium within 60 min, and the optimal pH was 3.0. The result of adsorption kinetics was simulated by the pseudo-second-order model. The adsorption equilibrium isotherm was well fitted with the Langmuir adsorption model. Furthermore, thermodynamics calculations revealed that the adsorption process was endothermic and spontaneous. Importantly, adsorption capacity of Cr(VI) obeyed the sequence of Fe₃O₄@SiO₂–G1 < Fe₃O₄@SiO₂–G5 < Fe₃O₄@SiO₂–G3, 3 generation of PAMAM (G3) was the optimal for adsorption capacity of Cr(VI). The maximum theoretical Cr(VI) adsorption capacity (q_m) of Fe₃O₄@SiO₂–G3 was 334.45 mg/g, and removal ration remained above 89.5% after five cycles of adsorption–desorption. Thus, Fe₃O₄@SiO₂–G3 is predicted to be an efficient adsorbent for the adsorption of Cr(VI) from aqueous solution, and the obtained results can help in the generation optimization during fabrication of dendrimer modified adsorbents.