A large-scale FePt nanocube monolayer was fabricated on silicon substrate by a simple spin-coating method. After sputtering a B4C thin film on the particle monolayer, these films were annealed at elevated temperature. Transmission electron microscope and magnetic property characterizations demonstrate that FePt nanocubes are well separated under high-temperature annealing and yield the magnetically attractive L10 phase without any indication of sintering under the protection of a B4C layer. Moreover, it is observed that the texture of the nanocube monolayer is lost in the high-temperature annealing. The magnetic properties with Hc=2200 Oe along the film normal and Hc=1700 Oe along the film plane are obtained for the Fe46Pt54 /B4C thin film.