In this work, we investigated synthesis, magnetic properties of silica coated metal ferrite, (CoFe2O4)/SiO2 and Manganese doped cobalt ferrite nanoparticles (MnxCo1-xFe2O4 with x= 0.02, 0.04 and 0.06)/SiO2 for possible biomedical application. All the ferrites nanoparticles were prepared by co-precipitation method using FeCl3.6H2O, CoCl2.6H2O and MnCl2.2H2O as precursors, and were silica coated by Stober process in directly ethanol. The composition, phase structure and morphology of the prepared core-shell cobalt ferrites nanostructures were characterized by powder X-ray diffraction (XRD), Fourier Transform Infra-red spectra (FT-IR), Field Emission Scanning Electron Microscopy and energy dispersive X-ray analysis (FESEM-EDAX). The results revealed that all the samples maintain ferrite spinel structure. While, the cell parameters decrease monotonously by increase of Mn content indicating that the Mn ions are substituted into the lattice of CoFe2O4. The magnetic properties of the prepared samples were investigated at room temperature using Vibrating Sample Magnetometer (VSM). The results revealed strongly dependence of room temperature magnetic properties on (1) doping content, x; (2) particles size and ions distributions.