Iron oxide nanometer powders were prepared by using sol-gel method and the supercritical fluid drying technology (SCFD) from inorganic salts. The characteristics of the iron oxide nanometer powders were characterized systematically. The results showed that the drying and crystallization of the production could be achieved in one step by SCFD method; furthermore, a highly dispersed, size uniformed and with better crystallization magnetite (Fe3O4) nanoparticles can be obtained. Phase transformation of the as-synthesized powders occurs at about 80°C, and only hematite (α-Fe2O3) can be obtained when being heated at temperatures higher than 400°C. The production synthesized by SCFD exhibits significant magnetic properties. As the heat-treated temperature increase, the magnetic properties of the sample decrease gradually.