In order to develop a new method of forming porous titanium dioxide, anodic oxidation and chemical etching of titanium were investigated in aqueous sodium hydroxide solution. From an observation by a scanning electron microscope, the formation of porous structure was ascertained at the surface of titanium plate after anodic oxidation. The pore size and film thickness of the formed TiO₂ were 50 nm∼1 µm and 100 nm∼1 µm, respectively, which were influenced strongly by reaction time, sodium hydroxide concentration, and bath temperature. In comparative experiments of chemical etching, porous TiO₂ was also formed at the surface of titanium plate. The pore size and film thickness of the TiO₂ formed by this method was similar to the films which obtained by anodic oxidation method. The results of X-ray photoelectron spectroscopy, X-ray diffraction, and X-ray fluorescence indicated that the films obtained from both methods were composed of amorphous TiO₂. An advantage of the anodic oxidation method is that the growth rate of oxide film can be controlled by applied current.