Abstract: Recently the solid state amorphization reaction （SSAR） induced by mechanical alloying （MA） or mechanical milling （MM） has been studied intensively because of its great potential for producing amorphous materials or nanostructured materials for technological purpose. However, the mechanism related to the process of MM or MA is still ambiguous. In the present work we have performed the ball milling of Fe-24Mn and Fe-24Mn-6Si mixed powders. By employing the X-ray diffraction and Moössbauer measurements, the composition evolution-during milling process has been investigated in details. A final product of mestable fcc structured, paramagnetic nanocrystalline alloy Fe-Mn or Fe-Mn-Si is obtained, implying a inter-diffusion mechanism of Fe and Mn through the surface of ultrafine powders. Compared with the ordinary bulk alloy of Fe-Mn-Si, the phase stability of the milled alloys is quite different.