Frequency dependence of power loss of MnZn ferrite was investigated in relation with the absolute complex permeability, μa(=μa-jμa″), in the frequency range 10 kHz–5 MHz and the temperature range 23–120 °C. Residual loss, Pr contributes more than half of the total power loss, Pc, at a frequency above 1 MHz and exhibits a close relationship with μa″. The specimen with grain size of 4 μm and ZnO content of 0 mol % indicates μa′ of 1280 and Pc of 140 kW/m3 at 1 MHz and 50 mT. In the second measurement at the remanent state after the dc magnetization of 400 A/m, these values, however, increased and then gradually recovered with time. This behavior is considered to be related to the diffusion of Fe2+ through cation vacancy. © 2000 American Institute of Physics.