The adsorption of N-2 on the perfect and defective graphite surfaces has been investigated employing density functional theory coupled with effective cluster models. It was found that N-2 can be chemisorbed at the edge site of armchair graphite surface and the N-N bond strength is weakened at the same time. Nevertheless, the adsorption at the edge site of zigzag surface is unstable in energy, which is distinctly different from the case of molecular oxygen as previously found at the same theoretical level. This can be attributed to the crucial effect of local edge carbon atoms arrangement of defect graphite surface. Similar adsorption behaviour could be expected for N-2 at the edge of single wall carbon nanotube. (c) 2005 Elsevier B.V. All rights reserved.