The effect of Al2O3 addition on the temperature dependence of the initial permeability and microstructure of NiCuZn ferrites is investigated. The temperature dependence of initial permeability decreases with an increase in Al2O3 addition. EPMA analysis reveals that Al2O3 dissolves in the NiCuZn ferrite grains but is not uniformly dispersed. Separation of the initial permeability into two components, one due to spin rotation and the other due to domain wall motion, reveals that with an increase in the Al2O3 addition, the temperature dependence of the domain wall motion component decreases, while that of the spin rotation component shows no notable change. This indicates that the decrease in the temperature dependence of initial permeability may be attributed to the influence of Al2O3 on the domain wall motion.