Understanding phenomena at the nanometre scale is of fundamental importance for future improvements of desired properties of nanomaterials. We report a detailed investigation of the microstructure and the resulting magnetic anisotropy by magnetic, transmission electron microscopy (TEM) and Mössbauer measurements of electrospun Cu_1−x Zn _x Fe₂O₄ nanofibres. Our results show that the electrospun Cu_1−x Zn _x Fe₂O₄ nanofibres exhibit nearly isotropic magnetic anisotropy. TEM measurements indicate that the nanofibres are composed of loosely connected and randomly aligned nanograins. As revealed by the Henkel plot, these nanofibres and the nanograins within the nanofibres are dipolar coupled, which reduces the effective shape anisotropy leading to a nearly random configuration of the magnetic moments inside the nanofibres; hence, the observed nearly isotropic magnetic anisotropy can be easily understood.