Fe60Pt40 nanoparticles have been successfully prepared by sonochemistry method from the solution of Fe(C2H3O2)2 and H2PtCl6. The as-prepared sample then has been annealed at temperatures from 450oC to 650oC. Annealed samples have ordered L1o phase with face-centered tetragonal (fct) structure and show hard magnetic properties. The nanoparticles annealed at 550oC show highest coervicity of 4.36 kOe measured at room temperature. The annealed-temperature dependence of the coercivity is consistent with the appearance of the order phase L1o in the samples.