FeSiB amorphous powder was produced by gas atomization, and subsequently toroidal-shaped FeSiB amorphous powder cores were prepared by cold pressing, using permalloy powder as an additive. The characteristics of gas-atomized FeSiB amorphous powder and high-frequency magnetic properties of the cores were investigated. FeSiB amorphous powder, exhibiting good soft magnetic properties with a saturation magnetization of 125 emu/g and a coercivity of 0.4 Oe, was successfully produced by gas atomization in the particle size range below 75 mum. The addition of permalloy powder was effective for compaction of FeSiB amorphous powder cores by cold pressing. Permalloy powder increases the effective permeability of the cores but deteriorates the high-frequency dependence of the permeability at high content