Ferrite compound of the chemical composition SrO · nFe2O3 (2.0<n<6) showed high magnetic properties comparable to that of SrO · 6Fe2O3 (M-ferrite). The saturation magnetisation Ms is 50 ∼75 emu/g in the range of n=6.0∼2.0. Coercive force iHc is 2.4kOe near n=6.0∼6.5 and n=1.5. Furthermore, SrO · nFe2O3 indicated hexagonal (M-type), orthorhombic and tetragonal phases in the range of n=6.5∼ 2.0, 2.0∼0.5 and less than 0.5, respectively. The fact means that a new magnetic phase is in existence near n=1.0∼2.0. Also, it is never recognized that the compound of chemical formula 3SrO · 2Fe2O3, which is described in the current phase diagram and have been prevailed for more than two decades, is in existence.