Abstract: Methane decomposition into hydrogen and carbon nanomaterials (CNMs) was carried out over Ni/ZSM-5 catalysts with different Ni contents at different temperatures. The yields of hydrogen and the CNMs increase significantly with Ni content and reaction temperature, but they level off at high temperatures when the Ni content is over 8 wt.%. The morphology of the CNMs strongly depended on the temperature. Multiwall carbon nanotubes were formed at higher temperature, while carbon nanofibers formed at the lower temperature. The catalytic activity of the Ni/ZSM-5 decreased with time.