We performed detailed ab initio study on DNA bases-functionalized semiconducting and metallic single walled carbon nanotubes (SWNTs). Local distortions and similar band structures of functionalized zigzag and armchair SWNTs were observed. It confirms that local atomic structural distortion on SWNTs caused by sidewall functionalization can drastically change the electronic structures of SWNTs, which may be an efficient pathway for band structure engineering. (c) 2005 Elsevier B.V. All rights reserved.