Magnetic zeolite hybrid systems have been developed for decontaminating radioactive wastewater from the reactors at Fukushima Daiichi Nuclear Power Plant. Superparamagnetic Fe₃O₄ and CoFe₂O₄ (MₓOy) nanoparticles were used to make core-shell MₓOy/SiO₂/zeolite (MSZ) systems. The MSZ were synthesised by 3 steps; preparing MₓOy particles by the solgel method firstly, the MₓOy particles were coated by SiO₂ by the Stöber method, then the MₓOy/SiO₂ particles were mixed with zeolite seeds of zeolite A, zeolite X or CHA-Na. In addition, MₓOy/Chabazite-Na (CHA-Na) was synthesised by a one-pot synthesis using an autoclave by crystallising the nanoparticles on preformed zeolite particles. The products were characterised by X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy. The elemental compositions of the cobalt ferrite, the MₓOy/CHA-Na and the MSZ were characterised by X-ray fluorescence. The magnetic properties of all products were measured by a magnetic property measurement system or vibrating sample magnetometer. The MₓOy particle diameters were calculated from the full width at half maximum of the X-ray peaks, observing by the TEM images, or measured by dynamic light scattering. The Cs or Sr adsorption capacities of the MₓOy/CHA-Na and the MSZ were characterised by inductively coupled plasma mass spectrometry.