Comparative studies on adsorption of atomic and molecular nitrogen indicate that in contrast to the previous results from tungsten bulk crystals, molecular chemisorption of N-2 is more stable than dissociative ones on tungsten anion clusters consisting of 8 atoms or less. Our result provides a new aspect in chemisorption on metal clusters, namely the energetically preferred channel of chemisorption -dissociative versus molecular - might be different for metal clusters and bulk surfaces. (C) 2003 Elsevier B.V. All rights reserved.