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 similar to 1 and 100 nm similar to 1 mu m, 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.