The electrical surface properties of ultrananocrystalline diamond/amorphous carbon composite films have been investigated by four-point probe I/V and Hall measurements, whereas impedance spectroscopy has been used to establish the electrical bulk properties of the films. It turned out that the surface is p-type conductive with a resistivity of 0.14 O cm and a sheet carrier concentration of 7.6 × 1013 cm-2. The bulk resistivity is higher by almost seven orders of magnitude (1.3 × 106 O cm). The bulk conduction is thermally activated with an apparent activation energy of 0.17 eV. From Cole-Cole plots of the impedance spectra it can be concluded that there are three different contributions to the bulk conductivity. In order to try to identify these three components contributing to the electrical bulk conduction, Raman spectra have been recorded at five different wavelengths from the IR to UV region. These measurements showed that the UNCD/a-C films consist of at least three components: diamond nanocrystallites, an amorphous carbon matrix, and trans-polyacetylene-like structures probably at the interface between these two. ; JRC.I.4-Nanobiosciences