We report the significant improvement of the stability of a copper nanowire (Cu NW)-based transparent conducting electrode (TCE). Our study confirms that in contrast to the common use of poly(vinyl pyrrolidone) (PVP) as a surface passivation agent, PVP facilitates the surface oxidation of CuNWs, which, in turn, severely affects the stability and performance of TCEs. To mitigate this issue, polyimide (CPI) is used as a protective layer for the fabrication of the Cu NW TCEs in the absence of PVP, which shows exceptional stability. The conductivity (resistivity) measurement confirms the stability of TCEs over a period of 90 days without any major degradation, while the conductivity of the reference TCE degrades completely after ∼15 days. In addition, we also demonstrate the device application of our Cu NW TCEs by fabricating a thin-film transistor (TFT) and an organic solar cell showing good operational stability. This study provides an insight into the role of PVP in the poor stability of Cu NWs and offers an alternative for the fabrication of Cu NW-based TCEs with improved stability.