Novel carbon tubes with a diameter of 200-500 nm and a length of 3-5 mu m have been synthesized via decomposing magnesium acetate. Novel carbon tubes have been analyzed and characterized using by X-ray diffraction, scanning electron microscope, transmission electron microscope, selected area electron diffraction (SAED) and Raman spectrum. The analysis results indicate that the graphitic degree of novel carbon tubes is low under our synthesis condition. Interestingly, inside these tubes, smaller Z-shaped carbon nanotubes (CNTs) are formed. The unusual morphologies have not been reported before. A tentative formation mechanism is proposed. (C) 2008 Elsevier B.V. All rights reserved.