A stable suspension of multi-walled carbon nanofibers (CNFs) in Al₂O₃ was prepared by adding ammonium polycarboxylate as a dispersant in an aqueous solution. A strong magnetic field of 12 T was applied to the CNFs/Al₂O₃ suspension to investigate the alignment of the CNFs. The result was that the CNFs in the matrix showed good alignment with the direction of the magnetic field. It was found that 0.5 mass% CNFs showed isolated alignment; in contrast, with 5 mass% CNFs there were mainly aligned bundles. The alignment was only seen with straight CNFs; curved CNFs showed no alignment in a magnetic field.