Abstract: Multi-wall carbon nanotubes (MWCNTs) were oxidized by soaking in mixed acids. Their microstructure and composition were characterized using transmission electron microscopy, atomic force microscopy, Raman spectroscopy and infrared spectroscopy. The influence of soaking time on microstructure and dispersibility of the cut MWCNTs in aqueous solution was investigated. Results show that the MWCNTs were oxidized at defect sites by the mixed acids and converted from highly tangled ropes into short, open-ended nanotubes with lengths of 200-1500nm. The isoelectric point was reduced from 4.5 to 3.5 due to hydroxyl and carboxyl groups on the surface and the open ends of the cut MWCNTs. The aggregation experiments and UV-vis absorbance spectra revealed that the cut MWCNTs can be best dispersed in an aqueous solution containing 0.1 wt.% of sodium dodecyl-benzenesulfonate when sonicated at a pH value of 2 for 40min.