Different ultrananosized diamonds obtained by shock-wave procedure and their nickel modifications were prepared and characterized by nitrogen physisorption, X-ray diffraction, Temperature-programmed reduction and IR spectroscopy. The catalytic behaviour of the modified composites in methanol decomposition to hydrogen, carbon monoxide and methane was also studied. The state of supported nickel particles as well as their reductive and catalytic properties strongly depends on the pretreatment conditions and the composition of the support. (c) 2006 Elsevier B.V. All rights reserved.