Carbon nanotubes (CNTs) filled with iron nanowires (Fe@CNTs) were synthesized by chemical vapor deposition on substrates with catalyst thin film coatings. The Fe@CNTs showed magnetic shape anisotropy due to the high aspect ratio shape of the nanowires. Here, the authors examined how the conditions of catalyst films (Fe and Ni), i.e., crystal structures and oxidation states, influenced the growth characteristics and the magnetic properties of the Fe@CNTs. The conditions of the catalyst films depended on whether vacuum deposition or sputter deposition was used. The coercivity of the Fe@CNTs was influenced by the conditions of the catalyst films. Their results showed that the sputter-deposited Ni film, which had the smallest grain size and lowest oxidation, showed the highest coercivity.