Aligned Cu nanowires were prepared by the reduction of aligned CuO nanowires in electron cyclotron resonance (ECR) hydrogen plasma at room temperature. They are single-crystalline and maintain the original alignment of the CuO nanowires. In contrast, the reduction of CuO nanowires by thermal processing in H(2) has failed to produce the expected Cu nanowires because of morphological changes and the coalescence of newly formed Cu nanowires, leading to the formation of films consisting of micron-sized particles. The morphological changes and coalescence of Cu nanowires result from their low melting temperature. The reduction mechanism under ECR conditions has been discussed. The application of ECR plasma can effectively avoid the high temperature demand for CuO reduction when using the thermal processing method. This template-directed method assisted by ECR plasma can be extended for the transformation of other one-dimensional (1D) nanomaterials at low temperature and low pressure.