We investigated effects of annealing time on structural and magnetic properties of the L1(0)- FePt nanoparticles synthesized by the `` SiO2- nanoreacter'' method. The magnetization and powder X- ray diffraction ( XRD) studies revealed that the annealing at 900 degrees C for 9 h could convert all of the FCC- nanoparticles to the well- crystallized L1(0) structure with a large coercivity while keeping their particle size. Such monodisperse and highly crystalline L10- FePt nanoparticles are a promising material for the realization of ultra- high density recording. (c) 2006 Elsevier B. V. All rights reserved.