Amorphous Fe78Si9B13 ribbons were milled in a high energy ball mill (8000 SPEX CertiPrep Mixer/Mill) with a ball-to-sample weight ratio of 5:1. The obtained metallic powders were sieved to a particle mean diameter 200–500, 75–200 and 25–75μm, and then annealed at 773K for 1h in an argon atmosphere to generate the nanocrystalline state and to reduce stresses induced by the milling process. The powders particles were mixed with silicone polymer to obtain toroidal cores. Polymerization process was made under magnetic field H=500A/m, and ensured a preferential orientation of a powder particles. Nanocomposite magnetic cores were made from the powder material obtained by high energy ball milling and influence of the metallic powder fraction on soft magnetic properties were investigated along with the possibility to control these properties with the size and amount of powder fraction. These results showed that the permeability of the powder and composite cores increases if the particle size increases. It was also found that the soft magnetic properties of the polymer composites can be controlled in a wide range and depends on mass fraction of the metallic powder Fe78Si9B13 in the composite, on shape and size of the powder particles and their orientation in composite.