A single step method for the simultaneous purification and opening of multi-walled carbon nanotubes is developed based on the particularities of the solid/solid reaction between NaOH and carbon materials. The redox reactions between carbon and NaOH proceed through the high reactive sites of the material. As a result, NaOH reacts only with the disordered carbon impurities and with the defected parts of the carbon nanotubes, i.e., essentially the tips, while the continuous graphitic layers of the nanotubes walls are not damaged. In addition, the metallic impurities and catalyst support are dissolved in NaOH. This one-step process represents an important breakthrough for a low cost production of very pure nanotubes. (c) 2005 Elsevier B.V. All rights reserved.