Graphene oxide (GO) was modified by polyamide-amine dendrimers (PAMAMs) via a grafting-from method, and then the GO/PAMAMs were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). The effects of the solution pH, the adsorption time, temperature and the initial concentration of Cu(II) adsorption onto GO/PAMAMs were studied. The kinetics and thermodynamics of Cu(II) adsorption were investigated with the Lagergren pseudo-first-order and pseudo-second-order kinetic model, Langmuir and Freundlich isotherm models were applied to simulate the experimental data. The experimental data showed that the adsorption process of Cu(II) onto GO/PAMAMs can be described with the Lagrangian pseudo-second-order kinetics model, indicating the adsorption process is chemisorption mainly. The experimental data of isotherm followed both the Langmuir isotherm model and the Freundlich model, which indicated that the adsorption was monolayer. The thermodynamics parameters of Gibbs free energy change (ΔG), enthalpy changes (ΔH) and entropy change (ΔS) were calculated and found to be positive, indicating that the adsorption of Cu(II) onto GO/PAMAMs was endothermic, non-spontaneous and entropic-adding.