The frequency dependence of complex permeability for various NiCuZn ferrites was investigated. The variation of complex permeability for NiCuZn ferrites can be presented as a form of a semi-circle, so called the Cole-Cole plot, and the relaxation phenomena were explained with various shapes of the plots. The relaxation time τ was calculated from f_rx, which is a relaxation frequency at µ"_max . Relations between anisotropy field H_A and relaxation time τ, initial permeability µ_i and H_Awere plotted to identify the frequency dependence of complex permeability.