Co0.5Ni0.5Fe2O4 nanoparticles have been synthesized by a stearic acid method. Core/shell Co0.5Ni0.5Fe2O4/SiO2 nanomaterials at varying amount of SiO2 are prepared by hydrolysis and condensation of tetraethyl orthosilicate (TEOS) precursor. The composition phase and average crystallite size have been characterized by means of X-ray diffraction. The particle structure and morphology of the core-shell nanoparticles are determined using transmission electron microscopy (TEM). The presence of Si-O-Si bonds for both coated samples is confirmed through Fourier transform infrared spectroscopic. Results show a decreasing saturation magnetization (Ms) when amount of TEOS is increased. The addition of SiO2 at first instance enhance the coercivity (H-c), and maximum Hc is observed when 0.4 mL TEOS is added. However, adding more SiO2 decrease the coercivity because the domain wall motion on the surface of nanoparticles is limited.