Nanocrystalline diamond films have been synthesized by microwave plasma enhanced chemical vapour deposition using H2/CH4 as the reactant gas. Nanocrystalline diamond thin films with surface roughness of 11.8 nm were obtained on silicon substrates. The nanocrystallinity, surface roughness and hardness were characterized by the Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy and Nano Indentation, respectively. The Raman spectra of the films exhibit a band near 1145 cm-1 and XRD patterns indicate the presence of nanocrystalline diamond. The hardness value of individual test point is approximately 102 GPa and the average hardness of thin film could reach 86 GPa.