This thesis is concerned with four main objectives: the opening and purification of carbon nanotubes and the side-wall functionalization of SWNTs and re-sealing of open.;.ended SWNTs. Chapter I introduces the structure, synthesis and special properties of carbon nanotubes. The latter part of the chapter reviews the present techniques for purification, functionalization (covalent and noncovalent), opening and filling of carbon nanotubes, especially SWNTs. Chapter 2 describes the opening of SWNTs and double-walled carbon nanotubes using molten sodium hydroxide (and other alkali and alkaline-earth hydroxides). The facts that hydroxide treated SWNTs and double-walled carbon nanotubes could be reversibly filled in solution and filling could be removed using aqueous washing under ambient conditions prove that hydroxide-treated SWNTs and DWNTs remain opened after the hydroxide treatment. Raman spectroscopy data shows there was no damage towards SWNTs structure after hydroxide treatment. Chapter 3 describes the use of steam at 1 atm. to open and purify SWNTs and MWNTs. HRTEM observations of various materials filled inside SWNTs and MWNTs using aqueous solutions prove that CNTs remain opened after steam treatment. Investigations of Raman and IR spectroscopy show that the steam treatment does not modify the CNTs tubular structure and avoids the formation of defects and functional groups. Chapter 4 demonstrates that steam purified SWNTs can be carboxylated readily on the side-walls by nitric acid treatment. Observations of IR, Raman spectroscopy and AFM show that, in contrast to as-made SWNTs treated by 3M HN03, structures of steam purified SWNTs were modified and functional groups were directly added onto the side-walls of the SWNTs after they had been treated with 3M HN03 under reflux and then washed with 4M NaOH. XPS results confirm the existence of COOH group on steam purified SWNTs after acid treatment and the aqueous NaOH washing. Chapter 5 demonstrates that the fullerene (C60) can be used to seal and block the open ends of open SWNTs with compounds inside. Investigations ~f EDX, HRTEM and STEM show that Fullerene (C60) could block both inorganic and organic compounds inside opened arc and CVD SWNTs using either vapour of C60 or ethanol solution of C60. Chapter 6 provides details of the experimental information and chapter 7 outlines the future work.