Synthesis of magnetic nanocomposite adsorbent from iron oxide with montmorillonite and bentonite minerals has been done. The aim of this research is to improve quality of adsorbent. The composite have been made by mixing Fe3+/Fe2+ salt solution within clay suspension. Iron cations will transform to iron oxides within composite after precipitation and heating process. The result of x-ray diffraction of composite showed that the iron oxide is of Fe3O4/γ-Fe2O3 phase. The magnetic properties measured with Vibrating Sample Magnetometer (VSM) showed that the composite have superparamagnetic properties. The composite is attracted to permanent magnetic field, after adsorbing a contaminant in water. Adsorbtion efficiency of these magnetic nanocomposite adsorbent is 80%-84% for thorium.