The orientation of carbon nanotubes (both SWNTs and MWNTs) has been demonstrated in magnetic field through modification with magnetic particles Fe3O4. The process of Fe3O4-modified CNTs composites is that acid-treated CNTs were refluxed in 2-pyrrolidone containing ferric triacetylacetonate at the solution's boiling point with the protection of nitrogen gas. The composites are ideal materials to help the CNTs to be aligned in magnetic field.