Magnetic nanoparticles (NPs) with modified surface are important materials for applications in biological systems. In this paper, FePt NPs have been prepared by electrodeposition method. After annealing at 700°C for 1 h under a mixture of 5% H₂ and 95% Ar atmosphere the FePt NPs exhibit the coercivity of 11.5 kOe. The FePt NPs are then coated with a layer of silica SiO₂ by using the Stober method assisted by mechanical waves originated from a sonicator. The FePt/SiO₂ NPs were easily bound with 3-aminopropyl-triethoxy-silance to have an amino surface. Analysis of transmission electron microscope reveales the core-shell structure of the NPs. [DOI: 10.1380/ejssnt.2011.536]