Poly(o-toluidine)/carboxylic acid groups contained multi-walled carbon nanotube (POT/c-MWCNT) nanocomposites has been successfully synthesized by in situ chemical oxidation polymerization using ammonium persulfate as an oxidant and sodium dodecyl sulfate as a surfactant in the absence of any added acid. The interaction between POT and c-MWCNTs and nature of chain growth have been investigated and explained according to the results of FT-IR and UV-visible spectroscopic analyses. Changes in the morphologies in the nanocomposites were measured using TEM and SEM techniques. The dc conductivity of POT was dramatically increased by introduction of the c-MWCNTs. The conductivity of nanocomposite was obtained in a range between 0.85 and 7.42 S cm(-1) for different concentrations of c-MWCNTs. The current-voltage (I-V) characteristics of these nanocomposites indicate a significant increase in current level with an increase in c-MWCNTs concentration in the nanocomposite. I-V characteristics plotted on a log-log scale showed that the charge transport mechanism is governed by Ohm's law. In addition, the increase of conductivity with respect to temperature revealed the semiconductor behavior of the nanocomposite. (C) 2011 Elsevier B.V. All rights reserved.