We have synthesized multi-wall carbon nanotubes by catalytic chemical vapour deposition (CCVD) method using an AB5 hydrogen storage alloy with diameter ranging from 38 to 150?m as a catalyst. The H2 uptake capacity of the carbon nanotubes prepared using an AB5 alloy as a catalyst is about 4 wt.% through to the pressure of 8MPa at room temperature. Differential thermal analysis thermogravimetric analysis (DTA-TGA) technique has been applied to investigate the effect of the diameters of the AB5 alloy catalyst of micrometer magnitude and the technique conditions in the CCVD process on the thermal properties of carbon nanotubes. As the catalyst diameter increases from 38 to 150?m, the average diameter of the prepared carbon nanotubes increases and the diameter distribution also enlarges. Electron microscope, Raman spectrum and thermal analysis all indicated that the catalyst sizes affect the diameter and the thermal properties of the carbon nanotubes. When the catalyst diameter increases, the initial weight loss temperature and the differential thermal peak temperature of the carbon nanotubes increases, which shows that the lager the diameter of the carbon nanotubes is, the higher the oxidation temperature, and the better the anti-oxidizablity. However, if the diameter of the catalyst is larger than 100m, the anti-oxidizablity does not rise anymore but tend to be invariableness. In the CCVD preparation process, the anti-oxidizability of the carbon nanotubes increases, when raising the ratio of the hydrogen gas in the reaction gas in our experimental range (4:1, 3:1, and 2:1, respectively).