Toroidal shape FeCuNbSiB nanocrystalline alloy powder cores were prepared by cold pressing using mechanically crushed and ball-milled powders,respectively.The morphologies and their effects on the magnetic properties of the compacted cores were investigated.Compared with ball-milled powders,mechanically crushed ones have more regular shapes and rounder edges,which lead to better inter-particle insulation.FeCuNbSiB nanocrystalline alloy powder cores fabricated from mechanically crushed powders exhibit remarkably lower core loss of about 248.2kW/m3 at 100kHz for maximum flux density Bm=0.1T,and more stable permeability up to 10MHz.Moreover,the dc-bias property could be improved significantly using mechanically crushed powders. Toroidal shape FeCuNbSiB nanocrystalline alloy powder cores were prepared by cold pressing using mechanically crushed and ball-milled powders, respectively. The morphologies and their effects on the magnetic properties of the compacted cores were investigated. Compared with ball-milled powders, mechanically crushed ones have more regular shapes and rounder edges, which lead to better inter-particle insulation .FeCuNbSiB nanocrystalline alloy powder cores fabricated from mechanically crushed-powder exhibits remarkably lower core loss of about 248.2 kW / m3 at 100 kHz for maximum flux density Bm = 0.1 T, and more stable permeability up to 10MHz. Moreover, the dc-bias property could be improved significantly using mechanically crushed powders.