CNTs/metal/Al2O3 nanocomposite powders were fabricated by thermal chemical vapor deposition (CVD) of C2H2 gas over metal/Al2O3 nanocomposite catalysts prepared by the selective reduction of oxide/Al2O3 powders. The yield and diameter of CNTs significantly depended on the kind of metal catalyst and catalyst size. X-ray diffraction (XRD) was used for phase identification. The morphology of CNTs was determined using field emission scanning electron microscopy (FESEM). FT-Raman spectroscopy revealed that the CNTs have single- and multi-walled carbon nanotubes structure. The relationship between the CNT yield/diameter and the characteristics of the composite catalyst was systematically investigated.