To lower the L1 0 ordering temperature of FePt thin films, a detailed understanding of the nucleation and growth processes of L1 0 ordered domains is of particular importance. In the present study, a nucleation activation energy E n = ͑0.5− 0.6͒ ± 0.1 eV and a growth activation energy E g = 0.9± 0.1 eV for the L1 0 ordered domains in the FePt thin films are determined by studying the individual annealing-temperature dependence of the nucleation and growth parameters of the L1 0 ordered domains. These data make a contribution to the understanding of the high L1 0 ordering temperature of FePt thin films for manufacturing magnetic recording media.