© 2015 Elsevier B.V. In this work, the core-magnesium ferrite (MgFe 2 O 4 ) nanoparticles were prepared by hydrothermal technique. Completed gold (Au) shell coating on the surfaces of MgFe 2 O 4 nanoparticles was obtained by varying core/shell ratios via a reduction method. Phase identification, morphological evolution, optical properties, magnetic properties and cytotoxicity to mammalian cells of these MgFe 2 O 4 core coated with Au nanoparticles were examined by using a combination of X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy, UV-visible spectroscopy (UV-vis), vibrating sample magnetometry and resazuri n microplate assay techniques. In general, TEM images revealed different sizes of the core-shell nanoparticles generated from various core/shell ratios and confirmed the completed Au shell coating on MgFe 2 O 4 core nanoparticles via suitable core/shell ratio with particle size less than 100 nm. The core-shell nanoparticle size and the quality of coating influence the optical properties of the products. The UV-vis spectra of complete coated MgFe 2 O 4 -Au core-shell nanoparticles exhibit the absorption bands in the near-Infrared (NIR) region indicating high potential for therapeutic applications. Based on the magnetic property measurement, it was found that the obtained MgFe 2 O 4 -Au core-shell nanoparticles still exhibit superparamagnetism with lower saturation magnetization value, compared with MgFe 2 O 4 core. Both of MgFe 2 O 4 and MgFe 2 O 4 -Au core-shell also showed in vitro non-cytotoxicity to mouse areola fibroblast (L-929) cell line.