According to the recent trend to raise the horizontal scan frequency to increase the image refinement of the High Definition TV and High Resolution Display, material with low core loss is required for the ferrite core for deflection yoke, which is secured even in the high frequency range. liking notice of the influence on the fine structure of Mg-Zn ferrite by the chemical com position and process, low temperature sintering was proceeded. Cu was added to the low loss Mg-Zn system ferrite. After select-ing MgO, ZnO, $Fe_2$$O_3$, CuO, MgO was substituted for CuO while varying the composition ratio. Then the sample was sintered for 3 hours between $980～1350^{circ}C$ Magnetic permeability, power consumption, shrinkage rate, core loss were measured. The start-ing temperature to test the shrinkage of the sample was nearby $900^{circ}C$, it increased according to the substitution process of Cu, and the firing temperature was lowered about $-50～-75^{circ}C$ alongside of the process.