Nickel and nickel-zinc ferrites are ones of the most abundant members of the soft magnetic materials. In the last few years, the interest in new methods of their preparation increases, because it is well known that the physical and chemical properties of these materials strongly depend on the preparing conditions. Powder samples of soft ferrites of NiFe2O4 and NixZn1-xFC2O4 were synthesized by a classical sintering procedure, planetary mill synthesis, and by a chemical procedure from complex compounds with acetylacetonato-ligands. Average particle sizes were 1 mum, 40 nm and 20x20x4 nm (slabs), respectively. All of the obtained materials were measured ill the frequency range of 7 - 12 GHz for the real and the imaginary part of permittivity and permeability, and the absorption coefficients were calculated. A concurrent analysis of the obtained values showed the influence of the method of synthesis, as well as the particle size on the absorption coefficients in the applied frequency range.