NiZn ferrites with different amounts of CuO have been synthesized by the conventional ceramic method and their spectra of complex permeability were investigated. The CuO contents affect the grain size and microstructure of NiZn ferrite obviously, which also result in the variation of saturation magnetization, magnetocrystalline anisotropy and porosity. Along with these relevant magnetic properties, the superposition of magnetizing mechanisms was testified to be predominant in determining the value of permeability. To manifest the increase of initial permeability, the permeability spectra of NiZn ferrite were resolved into two components including domain wall movement and spin rotation magnetization. The fitting results show that, with CuO contents increasing, the dominant contribution to dynamic magnetization changes from spin rotation magnetization mechanism to domain wall movement.Index Terms-NiZn ferrites, complex permeability, domain wall motion, spin rotation. 0018-9464 (c)