Well-assembled multi-wall carbon nanotube bundles are synthesized on sol-gel prepared Co-Mo-Mg-O catalysts by chemical vapor deposition (CVD) using CH4 as the carbon source. The yield (weighing over 15 times of the catalysts) is much higher than that using the conventional Co-Mg-O catalysts (weighing about 2 times of the catalysts). Mo-doping in the catalysts is considered to play an important role in the high yield and the assemblage of the carbon nanotube bundles. The effect of Mo is discussed in the article upon TEM, EDS and XRD characterizations of the products and catalysts. Effects of temperature and carbon source are also discussed.