Simultaneous production of hydrogen and carbon nanomaterials over Ni-loaded ZSM-5 catalysts via catalytic decomposition of methane was investigated. The effects of nickel particle size and reaction temperature on the hydrogen production, catalyst deactivation and the morphologies of the carbon nanotubes were investigated. Two catalyst were prepared: Ni/ZSM-5(300) - predominant size of the Ni particles 30-60 nm and nNi/ZSM-5(300) predominant size of the Ni particles 10-20 nm. The carbon nanotubes and nanofibers diameters produced over Ni/ZSM-5(300) was equal to 20-57 nm depending on the temperature. The average diameter of carbon nanomaterials obtained over nNi/ZSM-5(300) was about 15 nm regardless the temperature. Catalyst Ni/ZSM-5(300) was effective for the production of hydrogen via the methane decomposition at the temperature range 650-700 degrees C (constant hydrogen concentration about 55%). Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.