Magnetic graphene-Fe3O4 nanocomposites (G/Fe3O4) were fabricated by a facile and fast one-pot method and used as adsorbent to remove dye for wastewater using Rhodamine B as the adsorbate. Samples with different weight ratios of graphene oxide (GO) to Fe3O4 were prepared. The transmission electron microscopy results exhibit that the sizes of Fe3O4 nanocrystals decrease with the increasing of weight ratio of GO to Fe3O4. The magnetic characterization demonstrates that the saturation magnetization of nanocomposites decreases with the decreasing sizes of Fe3O4 nanocrystals. The investigation of adsorption kinetics and isotherm indicates the adsorption process can be described by Langmuir model and nanocomposites with the smaller sizes of Fe3O4 nanoparticles show better adsorption ability. Furthermore, the adsorbents could be recovered conveniently by magnetic separation and recyclable used after desorption process, and the decline in efficiencies of all samples is not more than 1.5% after five cycling runs. (C) 2015 Elsevier Ltd. All rights reserved.