Comparative study of reactivity of nano- and micro-sized alumina and nickel oxide, obtained by the electrical explosion of metal wires in oxidizing atmosphere, was carried out for the reactions NiO + MoO3, NiO + Al2O3, and Al2O3 + Bi2O3 by coupled anneals of ceramics, measurements of the conductivity of individual oxides and raw oxide mixtures, X-ray diffraction and differential thermal analysis. The total conductivity of nanostructured oxides was found lower than that of micro-structured ceramics. Mixing bismuth oxide with nano-structured alumina leads to stabilization of the low temperature polymorph alpha-Bi(2)A(3) up to 780 degrees C. The diffusion permeability of NiMoO4 layer grown at the surface of NiO ceramics, having submicron grains, was found 2 times lower if compared to NiMoO4 grown at micro-sized NiO ceramics. NiO and Al2O3 nano-powders preserve the high reactivity even when heated up to 1000 degrees C. The results are discussed in terms of size effects on the solid state reactivity of oxides. (c) 2005 Elsevier B.V. All rights reserved.