Purification and opening of carbon nanotubes has been carried out by treatment of as-made single-wall carbonnanotubes (SWNTs) with pure steam at 1 atm pressure. Treated samples have been characterized by high-resolution transmission electron microscopy and IR and Raman spectroscopy. Comparison between the steampurification and the standard nitric acid purification treatment shows that steam is less aggressive towarddamage to the tubular nanotube wall structure and forms fewer functional groups.