Polyaniline (PANI) was synthesized chemically, and then modified with magnetic iron oxide nanoparticles (Fe3O4 NPs). PANI and PANI-Fe3O4 NPs were used for removal of uranyl ions (UO22+) from aqueous solutions using a batch system. The synthesized adsorbents were characterized using FT-IR, SEM, BET and XRD techniques. From isotherm investigation, the maximum adsorption capacities (q(m)) were 150.0 and 108.0 mg g(-1) for PANI and PANI-Fe(3)O(4)NPs, respectively. The kinetics and equilibrium adsorptions were well-described by the pseudo-second-order kinetic and Langmuir model, respectively. Thermodynamic studies depicted that the adsorption of uranyl ions by PANI is a spontaneous exothermic process and in the case of PANI-Fe3O4 NPs, adsorption process is endothermic; therefore, the spontaneity is controlled by entropy.