Fe particles on the tops of carbon nanofibers immobilized on structured carbon microfibers (Fe-CNFs/CMFs) were prepared in situ by the catalytic decomposition of CO over Fe/CMFs catalyst, and their particle sizes, shapes and crystal phases were adjusted by changing the growth time of CNFs and the partial pressure of hydrogen. The as-obtained Fe-CNFs/CMFs were used as a catalyst for ammonia decomposition, which showed higher activity when they were prepared with the longer growth time of CNFs and the higher partial pressure of hydrogen. Moreover, the behavior of the typical Fe-CNFs/CMFs catalyst was also investigated when changing the experimental conditions. (C) 2013 Elsevier B.V. All rights reserved.