The process of preparation of FePt nanoparticles was investigated with emphasis on the effect of "growth temperature," at which the atomic diffusion between Pt-rich and Fe-rich phases leads to the formation of uniform nanoparticles. Consequently, it was demonstrated that by controlling, the growth temperature, the shape and crystallinity of FePt nanoparticles can be controlled. Oil the other hand, the size and composition were almost invariable at 5.6 +/- 0.5 nm and Fe53Pt47. respectively.