A simple procedure at room temperature using non-toxic and cost-effective precursors has been developed to prepare magnetic Prussian blue/graphene oxide (PB/Fe3O4/GO) nanocomposites for the removal of radioactive cesium in water. Taking advantage of the combined benefits of GO and magnetic PB nanoparticles, PB/Fe3O4/GO nanocomposites exhibit excellent removal efficiency (over 90% for 50 ppm Cs+) and rapid separation from an aqueous solution by an external magnetic field. In addition, the adsorption behavior of these adsorbents fits well with the Langmuir isotherm and the pseudo-second-order kinetic model. Sorption of 70.25% Cs+ to PB/Fe3O4/GO was finished in less than 30 min, and the maximum adsorption capacity was 55.56 mg g(-1). The improved adsorption efficiency and capacity of PB/Fe3O4/GO can be attributed to the anchoring technology, which reduced the aggregation of nanoparticles and increased the effective adsorption surface of the adsorbent. These nanocomposites present a high selectivity to Cs+ and extract it in trace amounts. The removal mechanism of Cs+ was revealed for the first time to be H+-exchange and/or ion trapping. The temperature and pH value both affect the sorption performance. The composites were stable in natural water, seawater, and acidic/basic solutions ranging from pH = 4 (HNO3) to 10 (NaOH) with negligible leaching of Fe.