Nanocomposite formation of metal-metal oxide systems by mechanical alloying (MA) has been investigated at room temperature. The systems we chose are the Fe 2O 3-M(M=Al,Ti,Zn,Cu), where pure metals are used as reducing agent. It is found that nanocomposite powders in which Al 2O 3 and TiO 2 are dispersed in Fe matrix with nano-sized grains are obtained by mechanical alloying Fe 2O 3 with Al and Ti, respectively. However, the reduction of Fe 2O 3 with Cu by MA is not occurred. And the system of Fe 2O 3-Zn results in the formation of FeO plus ZnO after 120 h of milling. It is also shown that the magnetic evidence for the solid state reduction by mechanical alloying through changes in saturation magnetization and coercivity.