gamma-Fe2O3 nanoparticles supported on MgO (macro-crystalline and nanocrystalline) were prepared by an easy single step thermal decomposition method. Thermal decomposition of iron acetylacetonate in diphenyl ether, in the presence of the supports followed by calcination, leads to iron oxide nanoparticles supported on MgO. The X-ray diffraction results indicate the stability of gamma-Fe2O3 phase on MgO (macro-crystalline and nanocrystalline) up to 1150 degrees C. The scanning electron microscopy images show that the supported iron oxide nanoparticles are agglomerated while the energy dispersive X-ray analysis indicates the presence of iron, magnesium and oxygen in the samples. Transmission electron microscopy images indicate the presence of smaller gamma-Fe2O3 nanoparticles on nanocrystalline MgO. The magnetic properties of the supported magnetic nanoparticles at various calcination temperatures (350-1150 degrees C) were studied using a superconducting quantum interference device which indicates superparamagnetic behavior. (C) 2011 Elsevier B. V. All rights reserved.