In this research, Fe3O4, Fe3O4/polystyrene and Fe3O4/polyaniline nanocompounds were prepared and compared on the removal of methyl orange from aqueous solutions. The chemical structures of the synthesized compounds were studied using FT-IR. The crystalline phase of Fe3O4, Fe3O4/polystyrene and Fe3O4/polyaniline nanocompounds was characterized by XRD. SEM was used for detecting morphology of the synthesized samples. The magnetic property of the prepared samples was successfully checked. The prepared nanocompounds were used to remove methyl orange as an anionic dye from aqueous solutions. Based on results, Fe3O4/polyaniline nanocomposite showed higher efficiency in the removal of methyl orange, which is partly due to the oppositely charged methyl orange and Fe3O4/polyaniline. Effective variables on the removal of methyl orange such as adsorbent dosage, pH, and contact time were studied and optimized. At the optimum situations the pH, catalyst dosage, and time were 3-4, 450 mg L-1, and 50 min, respectively. For detecting the type of adsorption isotherm, Langmuir, Freundlich, and Dubinin Radushkevich adsorption isotherms were studied. According to Langmuir model, Fe3O4/polyaniline magnetic absorbent showed the highest methyl orange adsorption capacity of 48.76 mg g−1. Kinetic studies proved that methyl orange adsorption was explained more accurately via pseudo-second order model compared to the pseudo-first order model. Under controlled reaction conditions, Gibbs free energy (ΔG˚) varied from -1.41 to -1.69 kJ mol-1, besides, the resulting ΔH˚ and ΔS˚ quantities were obtained 4.07 kJ mol-1 and 0.018 kJ mol-1K-1, respectively. Therefore, it can be considered that the adsorption of methyl orange onto the Fe3O4/polyaniline magnetic absorbent is a spontaneous and endothermic procedure.