Chaoite, a rare allotrope of carbon, is considered as a high-temperature phase abundant in circumstellar shells and is difficult to be synthesized at low temperature. However, in this study, chaoite phase was synthesized by quenching the pyrolysate of acetylene gas at low temperature and pressure. The typical morphology is a tube with 20–60 μm in diameter and more than 8 mm in length. Another interesting feature of these carbon macrotubes (CMTs) is the unexpected but clear intrinsic ferromagnetism. The ferromagnetism of sp-hybridized CMTs indicates that the sp-hybridized structure may be an origin of ferromagnetism. [ABSTRACT FROM AUTHOR]