The filling rate of Fe nanowires in carbon nanotubes (CNTs) was improved by a post-treatment which involved annealing and magnetic separation. The annealing process transformed gamma-Fe to ferromagnetic alpha-Fe, resulting in alpha-Fe-filled CNTs with improved magnetic properties. The Fe-filled CNTs were then separated from those unfilled CNTs due to the different attractive forces under magnetic field. Thermal gravimetric analysis (TGA) revealed that the purity of CNTs was improved after magnetic separation and the filling, rate can be LIP to 40.0 wt.%, which is increased about 8.1 % comparing with annealed CNTs. The Saturation magnetization of CNTs reached 31.45 emu/g after magnetic separation. (C) 2008 Elsevier Ltd. All rights reserved.