The functionalization of single walled carbon nanotubes (SWNTs) to introduce aqueous solubility for potential biological application of carbon nanotubes was investigated. These carbon nanotubes were found soluble in water, when hydrophilic oligomeric or polymeric molecules were attached. The solvation of nanotubes by water molecules and the mechanistic details of nanotubes were found to be analyzed. It was stated that highly water soluble SWNTs find valuable materials and biological significant applications.