The mixed oxide system Cr2O3MnOx (2 ≥ x ≥ 1.5) was investigated by X‐ray diffraction, by measurements of magnetic susceptibility, and by chemical determination of excess oxygen (BUNSEN'S method). The Presence of the antiferromagnetic oxides Cr2O3, β‐MnO2, α‐Mn2O3 and a ferromagnetic phase Cr1−yMnyO2 was stated. The formation of the latter with fourvalent chromium is explained by a lattice induction effect of the MnO2 (rutile type).