Ultrafine particles of IrO2-SnO2 binary oxides have been prepared by a sol-gel process consisting of hydrolysis and condensation of metal alkoxide alcoholic solutions. The rutile-type oxide solid solution of binary oxides, (Ir, Sn)O2 was formed after the calcination at 450-degrees-C. The a and c lengths of the lattice parameters linearly decreased with the increase of the iridium content. The Ir-Sn binary oxides were crystallized to the (Ir, Sn)O2 rutile-type phase at lower temperature than the iridium oxide to IrO2.