The ordered face-centered tetragonal (FCT) FePt nanoparticles (NPs) were successfully synthesized by the modified sol-gel method. The relationship between the annealing temperature (400, 500, 600 and 700 degrees C) and the structure and magnetic properties of the FePt NPs was discussed. And the possible growth mechanism was given in terms of atomic diffusion. Differential thermal analysis (DTA) showed the dehydration of various water molecules and combustion/decomposition of organic groups at the temperature below 600 degrees C. The X-ray diffraction (XRD) patterns revealed that as the annealing temperature increased to 500 degrees C, the L1(0) FePt NPs were formed as was indicated by the appearance of superlattice peaks (001) and (110). Moreover, based on the XRD results, we found that the chemical order parameters increased with the increase of the annealing temperature. The transmission electron microscope (TEM) images showed that the NPs produced at 700 degrees C had a mean diameter of 14 nm. The selected area electron diffraction (SAED) patterns of the samples annealed at 700 degrees C further demonstrated the synthesis of the L1(0) FePt NPs. The energy dispersive X-ray spectroscopy (EDS) analysis showed that no impurity phases existed in FePt NPs. The maximum coercivity (10,148 Oe) was obtained for the sample annealed at 700 degrees C. (C) 2013 Elsevier B.V. All rights reserved.