The Mn—Zn ferrite of the present invention contains basic components of 44.0 to 50.0 mol % (50.0 mol % is excluded) Fe2O3, 4.0 to 26.5 mol % ZnO and the remainder MnO, and has a real part &egr;′ of complex relative permittivity of 20,000 or less at 1 kHz and 50 or less at 1 MHz, thereby maintaining initial permeability in a wide frequency band, showing a low stray capacitance with a coil provided, and ensuring an excellent impedance in a wide frequency band. And a coil using the Mn—Zn ferrite as a magnetic core is also provided.