Ultrananocrystalline diamond (UNCD) films were deposited in microwave bell jar plasma reactor of ASTeX type. The applied mw power, pressure and substrate temperature were from 800 to 950 W, 7.5 kPa and from 1000 to 1100K. The deposition mixture were from 2 to 9.4 percent of methane in methane/hydrogen gas feed. Reactor was modified by rf capacitive discharge providing a negative dc self bias -125V at the substrate holder, for using bias enhanced nucleation (BEN) methode as a pretreatement method. The mechanical properties were studied by depth sensing indentation technique using FISHERSCOPE H100 XYp, the surface morphology of the deposited films was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM).The UNCD films exhibited high hardness of 70 GPa, elastic modulus of 375 GPa and very low roughness in the range from 9 to 18 nm.