Saturation magnetostriction was measured in polycrystalline excess‐iron NiZnCo ferrite over a broad range in compositions. The stoichiometric compositions were Ni2+1−x−y−zZn2+xCo2+yFe2+zFe3+2O4where 0<x<0.63, 0<y<0.019, 0.11<z<0.57. By oxidizing the samples, the Fe2+content was varied for a given molar composition from nearly the maximum allowable (stoichiometric) to 1&percent; of this maximum (oxidized). This study presents the first magnetostriction measurements on oxidized ferrite, which is used extensively in devices due to its low magnetic loss. A single ion model of the magnetostrictive contributions of Fe2+, Fe3+, Ni2+, and Co2+ions is formulated and compared to the data.