Sodium dodecyl sulfate (SDS) as a useful dispersing agent for pristine and purified multiwall carbon nanotubes (MWCNTs) to prepare MWCNTs-modified electrodes is described. The morphology of different MWCNTs is characterized by Transmission Electron Microscopy (TEM). Voltammetric responses at MWCNTs–SDS modified glassy carbon electrodes towards detecting H 2 O 2 are observed to compare the electrochemical action of MWCNTs in different circumstances. The best electrochemical action of pristine MWCNTs toward H 2 O 2 is at about 0.4 wt.% MWCNTs dispersed in 2 wt.% SDS aqueous solution modified electrode. The pristine and purified MWCNTs–SDS films display different electrochemical behaviors. In contrast to the properties of MWCNTs dispersed in distilled water, we conclude that SDS is helpful for the dispersion and the electrochemical action of pristine and purified MWCNTs.