The structural and electronic properties of fcc-TaN/SiNx nanocomposite thin films deposited by reactive magnetron sputtering have been investigated as function of the N and Si contents. Our studies have been mainly focused on three different types of nanocomposite TaxSiyNz films based on: nitrogen deficient fcc-TaN0.88, nearly stoichiometric fcc-TaN, and over-stoichiometric fcc-TaN1.2 with the Si contents in the range from 0 to about 15 at.%. The optical properties were investigated by ellipsometric measurements, while the DC. electrical resistivity was measured using the van der Pauw configuration at 300 K. The optical measurements were interpreted using the standard Drude-Lorentz model. The results showed that the electronic properties are closely correlated with both the compositional and the structural modifications of the TaxSiyNz films induced by the addition of Si atoms, and also depending on the stoichiometry of the starting fcc-TaN system. Thus, depending on both the nitrogen and the silicon contents, the fcc-TaxSiyNz films can exhibit room temperature resistivity values ranging from 10(2) mu Omega cm to about 6 x 10(4) mu Omega cm. Published by Elsevier B.V.