The behaviour of double stranded DNA molecules (dsDNA) attached to single walled carbon nanotubes (SWCNTs) was investigated by molecular dynamics simulations. We observe that disruption of short dsDNA helices is accelerated by the presence of SWCNT due to the establishment of pi-stacking interactions between the nucleobases and the sidewall of the nanotubes. These results are in good agreement with experimental evidences and confirm the mechanism of assembly between a single stranded DNA molecule and a SWCNT. Longer DNA molecules maintain the structure of a double helix although with the hydrogen-bonding network slightly altered on the relatively short time scale. (C) 2012 Elsevier B. V. All rights reserved.