The microstructure of a zirconia powder prepared from a gas-solid reaction was determined by SEM, EDXS, DRX and TEM analysis. At low temperatures (773 K) and up to 0.5 of reaction degree two types of particles were formed: a metastable tetragonal ZrO2 phase fixed on the Fe2O3 grain surfaces and isolated grains of monoclinic ZrO2 phase.