Copper (Cu) nanowires are inexpensive conducting nanomaterials intensively explored for transparent conducting electrodes and other applications. Here, Cu nanowires with approximately 40-nm diameter and a few hundreds of micrometers in length were selectively and facilely synthesized by a tetradecylamine (TDA)-assisted hydrothermal method. The Cu nanowires were highly flexible and were not oxidized by oxygen in air because of TDA's effective coating on the Cu nanowires, which was confirmed by SEM observation and FT-IR spectrum. Moreover, the Cu nanowires tended to self-assemble into close-packed bundles due to hydrophobic-hydrophobic interactions between alkyl chains of TDA. The roles of the reagents in the preparation process were investigated systematically. First, a proper concentration of TDA was essential to high-quality Cu nanowires and TDA had two effects: (1) TDA molecules could coordinate with copper cations to form Cu(II)-complex, which was then reduced to Cu by glucose; (2) In the growth mechanism of Cu nanowires, the newly formed side surfaces, {100} facets, was stabilized through chemical interactions with the nitrogen atom of TDA (capping agent). With regards to Cu source, when using cupric chloride, cupric nitride, cupric acetate, and cupric bromide, Cu nanomaterials with a variety of shapes such as nanowires, nanoparticles, hollow spheres, and nanoflakes could be obtained. Among these Cu sources, cupric chloride was a proper selection for the preparation of Cu nanowires. About reductant agents, glucose could be replaced by other reductant agents such as VC. The UV-Vis absorption spectrum showed that the Cu nanowires had an absorption peak at 580 nm and a slightly higher transmittance in the visible region. These Cu nanowires were expected to find widespread use in the applications such as fabrication of transparent electrodes for flexible electronics and display devices. This TDA-assisted hydrothermal method could be expanded to preparation of different types of Cu nanostructures.