Nanostructured ZnO has been receiving particular attention in recent years due to its great potential applications in electronic, optoelectronic and sensing devices. Considerable efforts have been done to fabricate ZnO nanowires, nanorods and nanotubes with diameters ranging from several ten to several hundred nanometers, and lengths from hundreds of up to several micrometers by using catalytic growth through physical or chemical vapor deposition and wet chemical methods. In particular, great interest have been focused on controllable synthesis and application of tubular ZnO owing to a high porosity and a large surface area, which are required to fulfill the demand of high efficiency and activity. In addition, high degree of regularity and alignment are important to control the properties, which are crucial for the fabrication of nanodevices.In these circumstances, we have fabricated selforganized nanoporous ZnO having an extremely high aspect ratio by a simple, high throughput and non-costly wet electrochemical process: anodization of Zinc plate in aqueous solutions. Recently, studies on the fabrication of TiO 2 nanotubes by anodic oxidation of titanium are reported intensively because of their exploitation in the fields of photo catalyst, die-sensitized solar cells and chemical sensors. It is well known that self-organized porous anodic alumina has significant potential application as a template for the nanofabrication of various devices. Here, we report the nanoporous structure of obtained anodic ZnO and photo catalytic properties as well as anodic film growth mechanism. Figure 1 indicates the cross section of porous ZnO film obtained by anodization in a solution of sodium hydroxide with the addition of ethylene glycol in the thickness of approximately 45 µm. As shown in the inset of high magnification image having a straight cellular structure, it is similar to the Keller's model of cylindrical anodic porous alumina, though the cell wall appears to be rather granular. Since the pore interval i.e., cell diameter is about 40 nm, the aspect ratio reaches up to around 1100. By prolonged anodization time, we could obtain a film with the thickness more than 90 µm. BET specific surface area of the anodic porous ZnO was approximately 28.5 m 2 / g. TFXRD measurement of the anodic ZnO before and after heat treatment at 300 ºC for 5 h shown in Fig. 2 reveals similar diffraction spectra of polycrystalline ZnO in both as grown and heat treated anodic porous ZnO films. From UV and visible light optical absorption spectra of thin and thick anodic ZnO films shown in Fig. 3, the absorption edge and the estimated band gap of both anodic porous ZnO films were 370 nm and 3.35 eV respectively. Photo catalytic activity of the anodic ZnO was ascertained by a methylene blue degradation test under UV irradiation at the wavelength of 254 nm.We have demonstrated the novel fabrication method of highly ordered nanoporous crystalline ZnO possessing straight channels with extremely high aspect ratio and high specific surface area by a sim...