The diameter and the growth rate of vertically aligned carbon nanotubes (CNTs) are controlled by modulating the size of catalytic particles using thermal chemical vapor deposition (CVD). The size of iron catalytic particles deposited on silicon oxide substrate is varied in a controlled manner by adjusting the condition of ammonia pretreatment. We found an inverse relation between the diameter and growth rate of carbon nanotubes. As the diameter increases, the compartment layers of bamboo-shaped carbon nanotubes appear more frequently. which is suitably explained by the base growth mechanism.