Fe2O3/Al2O3 catalysts were prepared by solid state reaction method using alpha-Fe2O3 and gamma-Al2O3 nano powders. The microstructure and surface properties of the catalyst were studied using positron lifetime and coincidence Doppler broadening annihilation radiation measurements. The positron lifetime spectrum shows four components. The two long lifetimes tau(3) and tau(4) are attributed to positronium annihilation in two types of pores distributed inside Al2O3 grain and between the grains, respectively. With increasing Fe2O3 content from 3 wt% to 40 wt%, the lifetime tau(3) keeps nearly unchanged, while the longest lifetime tau(4) shows decrease from 96 ns to 64 ns. Its intensity decreases drastically from 24% to less than 8%. The Doppler broadening S parameter shows also a continuous decrease. Further analysis of the Doppler broadening spectra reveals a decrease in the p-Ps intensity with increasing Fe2O3 content, which rules out the possibility of spin-conversion of positronium. Therefore the decrease of tau(4) is most probably due to the chemical quenching reaction of positronium with Fe ions on the surface of the large pores. (C) 2010 Elsevier B. V. All rights reserved.