An electrochemically active composite film which contains multi-walled carbon nanotubes (MWCNTs) incorporated with naphthol green B (NGB) was synthesized on glassy carbon, gold and indium tin oxide electrodes by potentiodynamic method. The presence of MWCNTs in the composite (MWCNTs-NGB) film modified electrodes mediates redox reaction of FeIII/II present in NGB, whereas no redox reaction of NGB occurred at the bare electrode. The electrochemical impedance spectroscopy studies revealed that NGB and MWCNTs present in MWCNTs-NGB composite film enhances electron shuttling between the reactant and electrode surface. The surface morphology of the MWCNTs and MWCNTs-NGB were studied using atomic force microscopy, which revealed that NGB incorporated and covered the MWCNTs on the modified electrode. The MWCNTs-NGB composite film exhibits promising enhanced electrocatalysis towards S2O8
2. The response of S2O8 2 at MWCNTs and MWCNTs-NGB composite films was measured using both cyclic voltammetry and i–t curve techniques. The linear concentration range of S2O8 2 determination at MWCNTs-NGB composite film was from 15.9 mM to 7.1 mM. The sensitivity of MWCNTs-NGB composite film towards S2O8
2 was 301.9 mA mM1 cm2, and the limit of detection was 6.9 mM. These above values are better than the values obtained at MWCNTs film.