The formation of a porous TiO2 layer by immersing Ti in 5 M NaOH at 303 K was investigated using electrochemical measurements, a scanning electron microscope, and grazing incident X-ray diffraction. The porous layer was readily obtained in the case of the presence of titanium hydride (TiH2) on the surface before immersion. The crystalline structure of the porous layer is composed of a mixture of the rutile and anatase type TiO2. The porous layer is hard to produce without the presence of TiH2. The TiH2 is directly changed to TiO2 by a dissolution reaction in alkaline solution. The presence of TiH2 on the surface is an important factor for the preparation of the porous TiO2 layer.