FePt:C composite films with large magnetocrystalline anisotropy are in-situ fabricated in this study by sputter deposition. The microstructure and magnetic properties of the films are investigated using X-ray diffraction, transmission electron microscopy and polar magneto-optical Kerr analysis. Well-defined grain boundaries and relatively uniform grain with mean diameter of 5.6 nm are obtained by doping. Results show an increase in magnetisation as the C content is increased while the exchange coupling indicated by the steep slope of the hysteresis loop at coercivity remained very large. Further increasing of the C content however decreased the magnetisation.