Various compositions of magnesium-copper-zinc (MgCuZn) ferrites were prepared via a co-precipitation method for the development of ternary property-composition diagrams. The diagrams were used to investigate the effect of various main components (MgO, CuO and ZnO) on the electromagnetic properties of MgCuZn ferrites system. Four electromagnetic properties were measured. These are initial permeability, quality factor, loss factor and resistivity. Analysis of the diagrams indicated that high MgO content was associated with the deterioration of the electromagnetic properties. Too much CuO led to the formation of Cu-rich precipitates that were detrimental to the electromagnetic properties. High ZnO content was necessary to obtain good magnetic properties of the ferrites. Hence, it was suggested that good electromagnetic properties on MgCuZn ferrites were attributed to low MgO, moderate CuO and high ZnO contents.