We investigated the electrical properties of Cu/TaOx/Pt structures, which were prepared by RF-sputtering at room temperature. Spectroscopic ellipsometry (SE) measurements revealed that the refractive indices of the TaOx thin films decreased with increasing oxygen-to-argon gas ratio during the growth. The transport analyses based on the Poole-Frenkel emission model yielded the dielectric constant of the TaO x layers; the results were consistent with the SE results. The Cu/TaOx/Pt structures exhibited bipolar resistive switching (RS), and less-oxidized samples showed a more reliable RS behavior than more-oxidized ones. The high-to-low resistance ratio was nearly 103, and the switching voltage was less than 1 V.