A nanotube material is obtained by the reaction of polycrystalline TiO₂ with concentrated NaOH solution for 20 h at 110 °C. From the contents of Na, Ti and the structural water determined, it is concluded that the nanotube material is Na₂Ti₂O₄(OH)₂, rather than TiO₂, TiO_x or H₂TiO₃. After treating with an HCl solution of pH 1, nanotube Na₂Ti₂O₄(OH)₂ can be converted to nanotube H₂Ti₂O₄(OH)₂. The crystalline structure of such nanotube materials belongs to an orthorhombic crystalline system. TEM results indicate that nanotube Na₂Ti₂O₄(OH)₂ is formed in the reaction stage of TiO₂ with concentrated NaOH solution. The formation process is discussed.