The influence of additions on the formation of nanocrvstalline Fe 3 Si by crystallization of amorphous Fe 7 6 . 5 B 7 Si 1 5 , 5 Cu 1 was investigated. The addition of V, Mo, W, Nb, Ta, Hf, or Nd leads to an increase of the crystallization temperature and to a reduction of the grain size. The grain size of the formed Fe 3 Si phase is correlated with the atomic diameter of the added element and decreases for 1 to 3 at% addition and for atomic diameter from 0.36 to 0.29 mn. The nanocrvstalline microstructure is caused by an increased number of growing and competing crystals due to reduction of diffusion and growth rate by the larger atoms. Contents of the addition >= 3 at % and atomic diameters >= 0.29 nrn do not reduce the minimal mean grain size of 15 nm of the Fe 3 Si phase, furthermore.