Mechanochemical interaction of tungsten with gallium was studied. Using x-ray diffraction and electron microscopy, it was shown that after mechanical activation of a W-Ga mixture for 1 min, gallium is completely spread, as a thin layer, onto the tungsten surface, while the longer activation leads to the formation of W(Ga) solid solution. Moreover, gallium was shown to be incorporated into tungsten lattice only if the grains reach a certain critical nanosize.