the results are presented for investigation of electrical conductivity of nano crystalline diamond (NCD) films with thickness of 0.5–0.6 microns grown on silicon Si(100) substrates by the CVD metho d using methane-hydrogen and methane-hydrogen-oxygen mixtures. By the metho d of heating in vacuum with using hydrogen analyzer AB-1, the concentration of hydrogen in the studied films was determined and the relationship between the content of hydrogen in the NCD film and its conductivity was estimated. It has been shown that high-temperature processing in vacuum at the temperature of 600°C leads to desorption of hydrogen from the films and to a significant increase in their resistance.