Isolated nanoparticles composed of bcc-Fe and L10-FePd have been fabricated by successive deposition of Pd and Fe onto NaCl substrate cleaved in air, and their structural characterization has been performed by transmission electron microscopy (TEM). Alloy composition was varied by changing the deposited Fe thickness in the thickness range between 2 and 7.5 nm with respect to the fixed Pd thickness of 1 nm. Post-deposition annealing lead to a formation of dual phase nanocomposite particles with the L10-type ordered phase and the bcc-Fe phase within each particle. The particle size little changed on annealing at 873K, indicating that both alloying and atomic ordering reactions proceeded within each nanoparticle. The size of the bcc-Fe region in Fe/FePd nanoparticles was measured from TEM images and its relation to the change of the maximum energy product was discussed.