Highly ordered TiO2 nanotube arrays (HOTNAs) were prepared from Ti foil by anodization using the ethylene glycol electrolyte containing 0.3% of ammonium fluoride with different concentrations of H2O2 at 30 V for 90 minutes. The structure, crystal phase, elements composition, and morphology of HOTNAs characterized by X-ray diffraction (XRD), energy dispersive X-Ray (EDX), ultraviolet-visible diffuse reflectance spectroscopy (UV/Vis-DRS), and field emission scanning electron microscope (FE-SEM) resemble the unique properties of TiO2 nanotube arrays in the anatase form with the individual tube diameter of 38-47 nm. The nanotube arrays have been applied for the CO gas sensor. The results show that both HOTNAs sensors synthesized using electrolyte with 0.3% H2O2/0.7% H2O and 1.8% H2O2/4.2% H2O were able to detect CO gas at the concentration range of 3000-20000 ppm. However, it is …