Self-assembly of DNA functionalized single-walled carbon nanotubes is studied and atomic force microscopy images show that the highly branched structures were formed for the DNA functionalized SWNTs. The formation of the branched structures can be explained by the hybridization of DNA attached to the ends and sides of SWNTs based on the DNA complementary sequence-specific pairing interactions. Statistical analysis shows that the interconnected degree of self-assembled SWNTs via DNA hybridization is seven times more than that of single strand DNA functionalized SWNTs, which can only have the non-complementary interaction. (c) 2005 Elsevier B.V. All rights reserved.