Epitaxial Fe4N thin films were grown on TiN buffered Si(001) substrate by dc reactive sputtering deposition at different substrate temperatures. Fe4N films epitaxially grew on TiN within the substrate temperature range from 250 to 350 °C. Lower than 250 °C there will be some other FexN compounds formed and higher than 400 °C there will be only Fe left. Fe4N is metastable and the postannealing process in vacuum will decompose Fe4N film to Fe. However, introducing 30% N2 in the postannealing atmosphere can stabilize the Fe4N up to 350 °C in the (Ar,N2) gas mixture. The surface roughness of the epitaxial Fe4N films decreases with film thickness. There is in-plane biaxial magnetic anisotropy of epitaxial Fe4N(001) on Si(001) with the  easy direction.