Abstract: Fe-29wt% Ni alloy ultrafine particles with different average sizes are prepared using the evaporation-condensation method. Under different pressures, the ultrafine particles are compressed into round small rings.As the pressure increases, martensitic volume fraction and specific saturation magnetization,σ_s, exhibit amarked increase,whereas corecivity, H_c shows a linear decline. The complex permeability varies with the Pressure. Its high frequency characteristic is much superior to that of the bulk.There is a close relationship between for pressure effect and the average size, d.

Key words: Fe-Ni alloy, ultrafine particle, pressure effect