Cetyltrimethylammonium Bromide (CTAB) and Dodecyl Trimethyl Ammonium Bromide (DTAB) were used to non-covalently functionalize Multi-Walled Carbon Nanotubes’ (MWCNTs’) surfaces. Transmission electron microscopy analyses evidenced the debundling effects of these two cationic dispersants on MWCNT aggregates. The intensity of G band relative to D band in Raman profiles of MWCNTs does not change substantially after the suspension, indicating the majority of the sp2 structure of MWCNTs is preserved well. There exists a critical concentration for both CTAB and DTAB in suspending MWCNTs, i.e. 0.1 g/l, which can be ascribed to the formation of dispersant micelles. CTAB is superior to DTAB in suspending MWCNTs at a concentration lower than the critical one, but a reverse trend is observed when the concentration is beyond the critical one; this is interpreted in terms of geometric features of alkyl chains.