Abstract: Au nanowires in 4H crystalline phase (4H Au NWs) are synthesized by colloid solution methods. The crystalline phase and surface structure as well as its performance toward electrochemical oxidation of CO before and after removing adsorbed oleylamine molecules (OAs) introduced from its synthesis are evaluated by high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), underpotential deposition of Pb (Pb-upd) and cyclic voltammetry. Different methods, i.e. acetic acid cleaning, electrochemical oxidation cleaning, and diethylamine replacement, have been tried to remove the adsorbed OAs. For all methods, upon the removal of the adsorbed OAs, the morphology of 4H gold nanoparticles is found to gradually change from nanowires to large dumbbell-shaped nanoparticles, accompanying with a transition from the 4H phase to the face-centered cubic phase. On the other hand, the Pb-upd results show that the sample surfaces have almost the same facet composition before and after removal of the adsorbed OAs. After electrochemical cleaning with continuous potential scans up to 1.3 V, CO electro-oxidation activity of the 4H Au sample is significantly improved. The CO electro-oxidation activity is compared with results on the three basel Au single crystalline surfaces reported in the literature, possible origins for its enhancement are discussed.