The paper describes magnetic core-shell nanoparticles (Fe₃O₄/SiO₂) synthesis that is an important stage of the manufacturing of smart material for targeted drug delivery based on the construction of the composite system mesoporous silica (MCM-41)-magnetite nanoparticles (Fe₃O₄)-immune cells (macrophages) for targeted drug delivery. The synthetic procedure for the fabrication of core-shell nanoparticles is modified in order to produce core-shell nanoparticles of the composition Fe₃O₄@SiO₂ in the superparamagnetic state. This is confirmed by the studies of phase composition and magnetic properties of this material. The dependence of the particles size of magnetite sol on initial concentration of iron chlorides is established. The conditions for the fabrication of core-shell Fe 3O₄@SiO₂ particles that are aggregatively stable in water are determined. Structural investigations of the samples demonstrate that the sizes of Fe₃O₄@SiO₂ particles lie in the range 30-50 nm.