A highly L10-ordered FePt film with a crystalline  orientation was prepared by SiO2 addition and rapid thermal postannealing on an oxidized Si substrate. In order to clarify the mechanism of L10 ordering and the crystalline orientation of a nonepitaxial FePt film, we investigated the effect of the preparation conditions on the film structure. The crystalline quality was strongly dependent on the additive amount of SiO2; a high chemical order without the distribution of the chemical order and a nearly perfect  orientation were obtained at a SiO2 composition of 10 vol %. The nucleation of L10 grains with a high chemical order and a  orientation was observed from an initial phase transformation stage at a low annealing temperature. The as-deposited FePt–SiO2 film consisted of a nanocrystalline structure in which SiO2 segregated at the grain boundaries; SiO2 diffused with the grain growth during thermal annealing. Because the in-plane tensile stress among the grains was a dominant origin for the  texture formation, two-dimensional grain growth with the annihilation of grain boundaries played a crucial role in the  ordering in nonepitaxial FePt films. It was also crucial to maintain a high stress during annealing, and the  ordering was enhanced by rapid heating.