Core-shell structured magnetic gamma-Fe2O3 coated with proton acid doping polyaniline nanocomposites (gamma-Fe2O3@PANI) were synthesized and used to adsorb arsenic(V) in aqueous solutions. Results indicated that the as-synthesized gamma-Fe2O3@PANI had a rapid adsorption rate and high adsorption capacity (0.502 mmol/g) for arsenic(V) removal in a pH range of 4 to 11. The adsorption process obeyed a pseudo-second-order kinetic model and was controlled by intraparticle diffusion and external liquid film diffusion. The Redlich-Peterson isotherm model was suitable to simulate the experiment data, indicating that both the physical and chemical adsorption occurred on the heterogeneous adsorption interfaces. The postulated adsorption mechanism of As(V) on the gamma-Fe2O3@PANI nanocomposite was possibly ascribed to electrostatic interaction and hydrogen bonding. These results suggest that the magnetic gamma-Fe2O3@PANI nanocomposite offers a promising candidate for the adsorption of As(V) in practical applications.