Active and stable Ni-Fe-SiO2 catalysts prepared by sol gel method were employed for direct decomposition of undiluted methane to produce hydrogen and carbon filaments at 823 K and 923 K. The results indicated that the lifetime of Ni-Fe-SiO2 catalysts was much longer than Ni-SiO2 catalyst at a higher reaction temperature such as 923 K, however, a reverse trend was shown when methane decomposition took place at a lower reaction temperature such as 823 K. XRD studies suggested that iron atoms had entered into the Ni lattice and Ni-Fe alloy was formed in Ni-Fe-SiO2 catalysts. The structure of the carbon filaments generated over Ni-SiO2 and Ni-Fe-SiO2 was quite different. TEM studies showed that "multi-walled" carbon filaments were formed over 75%Ni-25%SiO2 catalyst, while "bamboo-shaped" carbon filaments generated over 35%Ni-40%Fe-25%SiO2 catalysts at 923 K. Raman spectra of the generated carbons demonstrated that the graphitic order of the "multi-walled" carbon filaments was lower than that of the "bamboo-shaped" carbon filaments. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.