Carbon nanotubes (CNTs) were synthesized in the temperature range of 500-700 degrees C over cobalt (Co)- and molybdenum (Mo)impregnated CaCO3 catalysts using acetylene gas. The effects of Co-Mo/CaCO3 catalyst's calcination temperature and Co/Mo weight ratio on the carbon deposition rate were investigated. The synthesized CNTs were multiwalled nanotubes with variable outer diameters. They exhibited Type II isotherm, and their surface areas were in the range of 24.8-89.9m(2)/g. It was concluded that the Co/Mo ratio in the catalyst played an important role in the structure of carbon, Co was more active than Mo for the CNT growth, and the carbon deposition rate increased with an increase in the initial acetylene composition in argon, Co/Mo ratio, and the reaction and calcination temperatures. The highest carbon deposition rate was produced at a reaction temperature of 700 degrees C over the Co-Mo/CaCO3 catalyst synthesized at a Co/Mo ratio of 6 and a calcination temperature of 750 degrees C.