To provide MnZn ferrite and an MnZn ferrite core which can obtain high initial magnetic permeability over a broad frequency band.

In the surface of the fired body of MnZn ferrite contains, as auxiliary components, SiO2 of 0 to 0.005 pts.wt.(excluding zero), CaO of 0.02 to 0.2 pts.wt., MoO3 of 0.05 to 0.5 pts.wt., Bi2O3 of 0.005 to 0.1 pts.wt. and V2O5 of 0.005 to 0.1 pts.wt., based on 100 pts.wt. of the main components composed of MnO, ZnO and Fe2O3, a precipitated phase including MoO3 and CaO is contained, and, by controlling the average crystal grain size to 30 to 100 m and controlling the specific resistance of the fired body to 20 to 100 cm, the MnZn ferrite core in which initial magnetic permeability at 1 kHz is 12,000 and initial magnetic permeability at 150 kHz is 12,500 can be obtained.