Ferrites are one of the most studied materials around the globe due to their distinctive biological and magnetic properties. In the same line, anisotropic MnFeO nanoparticles have been explored as a potential candidate possessing excellent magnetic properties, biocompatibility, and strong magnetic resonance imaging (MRI) properties such as 2 relaxivity for magnetic field-guided biomedical applications. The current work reports the synthesis and morphological evolution of MnFeO nanocubes (MNCs) in a hydrothermal process using different volume ratios of water and ethanol. The synthesis protocol was designed to influence the properties of the ferrite nanocubes, for example, the variation in surface tension, dielectric properties, and the ionic character of the solvent, and this has been achieved by adding ethanol into water during the synthesis. Pristine MnFeO is formed with well-defined cubic to irregular cubic shapes with the addition of ethanol, as evidenced from XRD, field emission scanning electron microscopy, and porosity measurements. MNCs have been investigated for magnetic hyperthermia and MRI applications. Well-defined cubic-shaped MNCs with uniform size distribution possessed a high saturation magnetization of 63 emu g and a transverse relaxivity (2) of 216 mM s (Mn + Fe). Furthermore, the colloidal nanocubes showed concentration-dependent hyperthermic response under an alternating magnetic field. The MNCs are biocompatible but advantageously show anticancer activities on breast cancer MCF 7 and MDA-MB-231 cells.