NiZn ferrite coated with polyaniline, forming a composite structure, were synthesized by in situ polymerization at different aniline/NiZn ferrite weight ratio (Ani/NiZn ferrite = 1/1, 2/1, 3/1) and introduced into epoxy resin to be a microwave absorber. The spectroscopic characterizations of the formation processes of polyaniline/NiZn ferrite composites were studied using Fourier transform infrared, ultraviolet-visible spectrophotometer, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron spin resonance. Microwave absorbing performances were investigated by reflectivity in 2-18 and 18-40 GHz using arch method. The results showed that a wider absorption frequency range could be obtained by adding different polyaniline content in NiZn ferrite. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.