Coal tar pitch was treated at 773K in a constructed furnace system used under a magnetic flux density (B) of up to 10 T. The (002) X-ray diffraction peak intensity of the treated pitches increased with increasing B to approach a saturation value over 6 T. The magnetic-field dependence of the intensity was fitted by the order parameter calculated by assuming the cooperative orientation of several thousand carbon crystallites. This suggests that the hexagonal carbon layers should be oriented in parallel to the magnetic fields.