Multi-walled carbon nanotubes (MWNTs) were modified with poly(N-isopropylacryl- amide-co-acrylic acid) (P(NIPAAm-co-AA)), and the modified MWNTs can be homogeneously dispersed in aqueous solution. In addition, the MWNTs were endowed with thermo-responsive at 33°C . The MWNTs switched reversibly between aggregated and well-exfoliated states by using temperature as a stimulus. Moreover, the introduction of acrylic acid to copolymerize with N-isopropylacrylamide could greatly enhance the dispersing ability of MWNTs.