The FePt-based granular films for heat-assisted magnetic recording (HAMR) application have been developed by using the in-line sputter system. The microstructure development of the FePt-based HAMR media as a function of different doping elements and film thicknesses was investigated. The microstructure of the FePtC-Ag granular film showed a nonuniform grain size distribution. FePt-C granular films with small and uniform grains were obtained at different film thicknesses. It was found that the grain size slightly increased with the increasing film thickness. The well-isolated FePt grains with main grain size of 6.4 nm 0.6 nm and 6.86 0.8 nm were obtained for 6 and 10 nm FePt-C granular films, respectively. The developed FePt-C granular film with well-isolated FePt grains has the potential to be used as the recording media for HAMR application.