This paper discusses several structural, electrical and oxidation characteristics of co-sputtered Ta-Ru alloy films on oxidized Si-substrates. From X-ray examination, the Ta1Ru1 phase has formed and dominates in the compositions exeeding 54 at.% Ru content. The resistivity of the Ta-Ru thin films can reach a maximum of similar to 320 mu Omega cm in the composition range aia between 35 and 54 at.% Ru. After thermal treatment in air (600 degreesC, 1 h), Ru-rich samples show a less increase in resistivity than Ta-rich ones. The observed preferential oxidation of Ta in the Ta-Ru samples can be further interpreted by thermodynamic calculations. The Ta-rich surface oxide is believed to be responsible for the passivating ability of the Ru atom toward oxidation at high temperatures. This results in the Ru of the metallic state though the oxidation of Ta occurs.