Large scale production of impurity-free carbon nanotubes is a current challenge. For the bulk production of carbon nanotubes, the selection of an appropriate catalyst is also an important task. In this study, an aluminum oxide/iron nitrate catalyst was prepared by using a co-precipitation method. The surface morphology and composition of the catalyst were studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results were compared with a commercially available ferrocene catalyst. Multiwalled carbon nanotubes were grown by catalytic decomposition of ethylene over the catalyst via floating catalytic chemical vapor deposition. The yield of nanotubes increased with an increase in the mass of aluminum oxide/iron nitrate but remained unchanged with an increase in ferrocene mass. The yield of carbon nanotubes remained between 68 and 93, which was much higher than obtained with only ferrocene (4). In case of ferrocene, rather affecting the product yield, the catalyst mass affected the diameter of the nanotubes. The tube diameters were between 20 nm and 34 nm for aluminum oxide/iron nitrate and between 39 nm and 71 nm for ferrocene. © 2015, Copyright Taylor & Francis Group, LLC.