In present work, o-toluidine (OT) monomer is electropolymerized in the presence of an aqueous acidic solution containing Triton X-100 (TX-100) non-ionic surfactant onto multi-walled carbon nanotube paste electrode (CNTPE). The as-prepared substrate is used as a porous matrix for dispersion of Ni (II) ions by immersing the modified electrode in a nickel (II) sulfate solution. The modified electrodes are characterized by field emission scanning electron microscopy (FE-SEM) and electrochemical methods. The electrochemical characterization of the nickel/poly (o-toluidine)/Triton X-100 film modified carbon nanotube paste electrode (Ni/POT (TX-100)/MCNTPE) exhibits redox behavior of Ni(III)/Ni(II) couple in alkaline medium. It has been shown that POT/TX-100 film at surface of the CNTPE improves efficiency of the catalyst toward formaldehyde electrooxidation. Moreover, the effects of various parameters such as TX-100 concentration, formaldehyde concentration, OT concentration, film thickness and accumulation time on the electrooxidation of formaldehyde as well as long-term stability of the Ni/POT (TX-100)/MCNTPE have also been investigated. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.