The present authors found that Mn–Zn ferrites containing Er2O3 had improved values of σs (specific magnetization) and amplitude permeability. Samples with different addition amount of Er2O3 were sintered at 1180 °C. The results show that Er2O3 addition from 0.02 to 0.1 wt % causes the amplitude permeability to increase from 1070 to 2180. The magnetization can be increased from 91.6 to 92.8 emu/g within the range 0.02–0.1 wt %. Furthermore, the effect of Er2O3 addition was investigated in detail by power‐loss analysis and scanning electron microscopy examination of microstructure. We found that samples with Er2O3 less than 0.04 wt % exhibit power loss similar to the sample without Er2O3 addition and with SiO2–CaO contents. Thus we conclude that the amplitude permeability and specific magnetization of Mn–Zn ferrites for high‐frequency and high‐power use were improved by a small Er2O3 addition (≪0.04 wt %).