Nanosized spinel ferrite (AFe(2)O(4), A = Ni, Fe, Zn) catalysts are prepared by 'bottom-up' approach, i.e. first forming the nanostructured building blocks and then assembling them into the final material with average particle size of 7-12 nm and surface area of 80-100 m(2)/g. The synthesized nanocrystallites were characterized by thermal analysis, powder X-ray diffraction, transmission electron microscopy and inductively coupled plasma (atomic emission spectroscopy) technique for evaluating phase, structure and morphology and stoichiometry. These materials were found to be very good catalysts for the oxidation of styrene to benzaldehyde in the presence of hydrogen peroxide. Of the several catalysts tried, magnetite (Fe3O4) has shown to have the best catalytic activity for the above reaction. The effects of solvent medium used, styrene: hydrogen peroxide molar ratio, reaction temperature, time and reaction atmosphere required for the complete conversion of styrene to benzaldehyde were also studied. Based on our findings, a plausible mechanism involved in the catalytic reaction is proposed. (c) 2005 Elsevier B.V. All rights reserved.