Ultra-long copper microwires have been prepared by a facile hydrothermal method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), nitrogen sorption isotherms. The results show that the ultra-long copper microwires have a five-fold symmetric twin crystal structure. It is proposed that both the selective adsorption of CTAB on {100} facets and the internal tension of copper crystals synergistically lead to the formation of the copper microwires. Moreover, the apparent rate constant (ka=0.00484 min-1) of copper microwires is 3.5 times as high as that (ka=0.0014 min-1) over bulk Cu for for the H2O2-assisted RhB decoloring reaction, which has been mainly ascribed to its larger surface area and microscale size. The adopted method can be potentially used for mass production of copper microwires because of the high yield and the simple operation.