A new method, gamma-irradiation, has been developed to prepare nanocrystalline,metal, alloys, metal oxide, and composites. The reactions of gamma-irradialion on a rod type FeOOH in the presence of isopropanol and water have been investigated. In the initial stage of the gamma-irradiation, FeOOH was turned into magnetite. With. the continued gamma-irradiation, (over 50000 Gy), FeOOH disappeared and the product was a single phase of magnetite. XRD, SAD, LRTEM and HRTEM,were used to characterize the structure and to determine their morphology,,respectively. The VSM spectrum was obtained to study magnetic properties of the products.