Liquid-phase adsorption of Cu2+ ions onto magnetic Fe3O4@graphene oxide (GO) composites, prepared by a co-precipitation approach, has been investigated. This synthesis method is capable of depositing highly crystalline Fe3O4 nanoparticles onto GO sheets. The adsorption temperature and the weight ratio of Fe3O4 nanoparticles to GO sheets are found to be crucial factors affecting the adsorption performance. The pH value of the aqueous solution has a strong influence on the adsorption capacity of Cu2+ ions. The Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) adsorption models were adopted to fit the adsorption isotherms. The deposition of magnetite enhances the equilibrium rate constant (Langmuir model) and the adsorption energy (D-R model). The analysis of thermodynamic parameters reveals that the adsorption of Cu2+ ions is a favorable and spontaneous process. However, a moderate density of magnetite onto GO substrate is essential for the design of Fe3O4@GO adsorbents for efficient removal of metal ions from an aqueous solution.