A Mn—Zn ferrite and a coil component are provided which obtains a low core loss in a frequency band above 1 MHz and even above 5 MHz and which can duly function in such a high frequency band. The Mn—Zn contains as basic components 44.00 to 50.0 mol % Fe2O3 (50 mol % excluded), 4.0 to 26.5 mol % ZnO, and remainder MnO, and has a dielectric loss tan of 0.3 or less at 1 kHz, and a complex relative permittivity of 1,000 or less at 1 MHz, whereby a core loss decreases in the high frequency band.