In this study, multiwalled CNT bundles were synthesized with an alumina-supported Fe2O3 catalyst by using a floating catalyst chemical vapor deposition (FCCVD) technique. The metal catalyst was synthesized by dispersing Fe2O3 on alumina support. Ethylene molecules were decomposed over different amounts of metal nanoparticles in a FCCVD reactor. The CVD temperature was elevated from 600°C to 1000°C. The large active surface area of the metal nanobuds promoted the decomposition of a carbon precursor and the fast growth of CNT bundles. Least dense bundles of varying heights were observed at lower CVD temperatures of 600°C and 700°C. At 800°C, CVD process conditions were found suitable for the fast decomposition of hydrocarbon. The relatively better yield of well-structured CNTs was obtained with a catalyst weight of 0.3 g at 800°C. Above 800°C, CNT forests start losing alignment and height. The forest density was also decreased at temperatures above the optimum. The elemental composition of CNT bundles revealed the presence of carbon, aluminium, oxygen, and iron in percentages of 91, 0.76, 8.2, and 0.04, respectively. A very small ID to IG ratio of 0.22 was calculated for CNTs grown under optimized conditions. © 2019 Shazia Shukrullah et al.