We have performed the first-principles calculations on the structural, electronic, and magnetic properties of ferromagnetic nanowires encapsulated inside silicon carbide nanotubes (SiCNTs). The results show that three types of the Fen (n = 5, 9, and 13) nanowires encapsulated inside the (8,8) SiCNT are all exothermic. For both Fe5@(8,8) and Fe9@(8,8) systems, the initial shapes are preserved without any visible changes after optimization. But for the Fe13@(8,8) system, the initial shapes are distorted for both nanowire and nanotube. There are more bands crossing the Fermi level for the minority spin than those for the majority spin, indicating the spin polarization transport process can be achieved in these Fen@(8,8) systems. The magnetism is mainly confined within the inner Fe nanowires for all three Fen@(8,8) systems. Our results reveal that the Fen@(8,8) systems have high spin polarization and magnetic moment and stably exist in atmosphere for long time, and thus can be expected to have potential applications in building nanodevices.