Carbon nanotubes (CNTs) were treated in air microwave plasma at three different microwave powers 80, 100 and 150 W. The effects of the treatment on the Structure of CNTs and the dispersion of Ru particles supported on CNTs were evaluated using XRD, N-2 physisorption, FTIR, TPD, XPS, TEM and CO chemisorptions. The results show that the bulk structure and the texture of the CNTs were unchanged, but phenolic hydroxyls and carboxyls appeared on the surface. The total concentration of these groups increases with the microwave power to 100 W, then decreases. The phenolic hydroxyls and carboxyls on the CNTs interact with Ru ions during the preparation of Ru/CNTs resulting in highly dispersed Ru particles. The activity of Ru/CNTs for ammonia decomposition depends on the dispersion of Ru particles, but is negatively affected by any remaining oxygen-containing groups on the surface. (C) 2009 Elsevier B.V. All rights reserved.