For basic understanding of how to produce a homogeneous distribution of nano-scale oxide particles, we have applied dual ion-implantation to make a super-saturation of oxide-forming elements. Y + and O + ions were implanted into ferritic alloys at room temperature. Both in situ annealing in an electron microscope for thin samples and conventional annealing for bulk samples were carried out at 300-1300 K. Nano-particles of Y 2O 3 precipitated during annealing, where the starting temperatures for the nucleation and growth depended on the annealing methods. In thin specimens the growth and nucleation of Y 2O 3 started at 573 and 613 K. In bulk specimens, the growth and nucleation shifted to higher temperatures. Compared with conventional Mechanical Alloying, it is concluded that dual ion-implantation can produce much finer distributions of nano-scale oxides. In order to explain these results, we emphasize the roles of super-saturated elements and lattice defects.