The magnetic extraction, purification, labeling and detection of biomolecules and cells are widely applied recently. In addition, the synthesis of silica magnetic particles for biomedical applications has been developed. In this paper, the synthesis of silica-coated magnetic nanoparticles was performed through three steps. First, an organic ferrofluid was prepared by the coprecipitation technique. Then it was used to prepare the magnetic emulsion. Finally, the hydrophobic magnetic nanoparticles were coated by silica shell using the sol-gel process. The prepared particles during the three steps were characterized in term of morphology, chemical composition and magnetic behavior under magnetic field. The results confirmed the formation of silica-coated magnetic nanoparticles, which are superparamagnetic even after silica encapsulation. The particles size was adjusted in order that a magnetic field can easily separate the particles at the same time they are stable colloids. Obtained particles can be used to extract and purified the nucleic acids, immobilized the enzymes, proteins and antibodies or to label the bacteria cells.