Vertically aligned carbon nanotubes (CNTs) are grown on iron-deposited silicon oxide substrates by thermal chemical vapor deposition (CVD) of acetylene gas at the temperature range 750-950 degreesC. As the growth temperature increases from 750 degreesC to 950 degreesC, the growth rate increases by four times and the average diameter also increases from 30 mn to 130 nm while the density decreases by a factor of about two. The relative amount of crystalline graphitic sheets increases progressively with the growth temperature and a higher degree of crystalline perfection can be achieved at 950 degreesC. This result demonstrates that the growth rate, diameter, density, and crystallinity of CNT can be controlled with the growth temperature.