A novel process for the preparation of Fe3O4-loaded activated carbon (MY) was developed using waste biomass. The key point of the synthetic strategy was that the carbonization, activation and Fe3O4 loading were accomplished simultaneously. The low-cost composite was characterized and used as an adsorbent for arsenate removal from water. The results showed that the Fe3O4 particles were uniformly deposited on the surface of the composite. The composite exhibited high surface area of 349 m2/g, pore volume of 0.20 cm3/g and iron of 39 wt.% for arsenate adsorption. As an adsorbent, higher temperature favored the adsorption capacity and the adsorption process was well fitted by pseudo-second-order model. The composite showed an excellent adsorption capability for arsenate with a maximum adsorption capacity of 204.2 mg/g at pH 8.0 and the adsorption process followed the Freundlich isotherm model well. In addition, the composite exhibited a saturation magnetization of 47.67 emu/g, which allowed it to be easily recovered by an external magnetic field after the adsorption process.