Supercritical fluids possess unique characteristics that make them effective and environmentally friendly processing media for nanomaterials. Of the nanomaterials of widespread applicative interest, iron oxide nanoparticles have an important role. The importance of iron oxide nanoparticles is due to the multidisciplinary nature of their industrial applications. However, the use of supercritical fluids in the processing of iron oxide nanoparticles is not well-recognized. In this review, special emphasis is placed on applying supercritical fluids technology for iron oxide nanoparticle synthesis, mesoporous iron oxide composite generation, and encapsulation of iron oxide nanoparticles. The role of supercritical fluids in hydrothermal synthesis, nanoscale casting, supercritical drying, and antisolvent techniques is discussed in detail. Finally, potential applications of supercritical fluid technology for the processing of iron oxide nanoparticles are presented.