CuxZn0.5-xMg0.5Fe2O4 (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) ferrite nanoparticles are synthesized via thermal treatment technique using polyvinyl alcohol (PVA) as a capping agent. The effect of Cu2+ ions substitution on the magnetic and structural properties of ZnMg ferrite nanoparticles is assessed. X-ray diffraction (XRD) results prove the formation of spinel cubic ferrite with nanocrystalline structure. It is observed by increasing Cu2+ ions content in Cu2+-substituted ZnMg ferrite samples, the lattice constant decreases. The field-emission scanning electron microscopy (FESEM) micrographs indicate that all samples have sizes in nanometer scale with almost spherical morphology and ZnMg ferrite nanoparticles size is increased as the result of Cu2+ substitution. Magnetic data show that by increasing in Cu2+ content, the saturation magnetization (Ms) increases up to x=0.3 and then declines with the addition of more Cu2+ ions in the samples. To assess the heat release of Cu2+-substituted ZnMg ferrite nanoparticles, an alternating magnetic (AC) field is applied. The results show an upward trend for the samples in the temperature vs time chart, as a result of increasing in Ms of the samples. The Cu0.3Zn0.2Mg0.5Fe2O4 sample exhibits a temperature increase up to 43 degrees C during 510seconds in the exposure of 125Oe magnetic field intensity. The cell compatibility of the samples is investigated using osteoblast-like cells (MG63). Results show that the substitution of Cu2+ significantly affects the cell compatibility of the ZnMg ferrite nanoparticles.