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The binary Fe-Si elemental powders mixture (1:2 in atomic proportion) has been milled for different milling times in an attrition mill. The phase characterization of mechanically alloyed powder was investigated using the chemical method of differential dissolution (DD) and the X-ray diffraction (XRD) method. In powder specimens milled for more than 15 hr, ε-FeSi and unreacted Si were observed. The formation of a supersaturated solid solution of Si in ε-FeSi induced by mechanical alloying (MA) was also verified. The lattice parameter of the ε-FeSi of as-milled powders changed from 4.4876 Å to 4.4668 Å according to the increase of MA time. Based on the results of the DD analysis, unreacted Si could be classified as (1) crystalline Si, (2) Si supersaturated in ε-FeSi, or (3) amorphous Si. Therefore formation of the β-FeSi 2 after annealing could be explained by the reaction between the ε-FeSi and the Si classified into types (1) and (2). It seemed that the amorphous Si induced by MA did not react with the ε-FeSi during annealing at 700 o C.