We demonstrate that the crystalline quality of multi-walled carbon nanotubes (MWCNTs) is better estimated by the apparent activation energy of the oxidation reaction, obtained by kinetic analysis in quasi-isothermal conditions, than by the peak-temperature position in the derivative mass loss curves. This is proven by the existence of a good correlation, reported for the first time herein, between apparent activation energy and G'-band to D-band intensity ratio derived from micro-Raman spectroscopy, which is largely accepted as an indicator of the overall MWCNT crystalline quality. In contrast, no clear reliance is found between G'/D intensity ratio and the peak-temperature position in the derivative mass loss curves. These conclusions were drawn after investigation of a large number of commercially available and laboratory prepared MWCNTs.