Ordered L1₀ and high coercivity FePt nanoparticles were successfully synthesized via a chemical method using pre-synthesized Au nanoparticles as nuclei seeds. The size of the Au nanoparticles seems to play a significant role in the formation of the tetragonal phase (L1₀) FePt colloidal nanoalloys. Seeding with ∼12 nm diameter monodispersed Au nanoparticles in the reaction mixture was found to lead to partial L1₀ FePt particles with 2.8 kOe coercivity at room temperature, while seeding with ∼6 nm Au nanoparticles leads to the formation of well L1₀ ordered FePt colloidal particles with 8.8 kOe coercivity at room temperature, one of the highest values for the direct liquid phase synthesis of L1₀ FePt colloidal particles. Furthermore, seeding with smaller Au particles decreases the ordering temperature from 360 °C to 300 °C leading to the formation of more uniform well-shaped nanoparticles.