Single-walled and multiple-walled carbon nanotubes were functionalized with poly(vinyl alcohol) (PVA) in esterification reactions. Similar to the parent PVA, the functionalized carbon nanotube samples are soluble in highly polar solvents such as DMSO and water. The common solubilities have allowed the intimate mixing of the functionalized nanotubes with the matrix polymer for the wet-casting of nanocomposite thin films. The PVA−carbon nanotube composite films are of high optical quality, without any observable phase separation, and the carbon nanotubes in the films are as well-dispersed as in solution. The functionalization of carbon nanotubes by the matrix polymer is apparently an effective way in the homogeneous nanotube dispersion for high-quality polymeric carbon nanocomposite materials. Results from characterizations of the solubilized carbon nanotubes and the nanocomposite thin films are presented and discussed.