Carbon nanotubes (CNTs) were prepared using different carrier gases,with ferrocene as the catalyst precusor and acetylene as the carbon source. The effects of ammonia and nitrogen as carrier gases on the structure and morphology of CNTs were investigated. Transmission electron microscope (TEM),high-resolution electron microscope (HRTEM),scanning electron microscope (SEM) and X-ray diffraction (XRD) were employed to characterize the products and the catalyst. Experiment results show that the CNTs grown in N2 gas exhibited cylindrical and tubular structure,while a bamboo-like structure was observed for the CNTs grown in NH3 gas. Moreover,vertically aligned CNTs were obtained on an Al2O3 disk when NH3 was used as the carrier gas. The carrier gas also exerted influence on the shape of the catalyst. Based on the theory of active centers of catalysis and combined with the particle shape of the catalyst,a growth model for the vertically aligned CNTs on the substrate is given.