The electrochemical performance of thin film boron-doped diamond (BDD) electrodes deposited on either single crystal p-type Si (Si/BDD) or Nb (Nb/BDD) substrates have been investigated for the electrooxidation of azo-dye Acid Violet 7 (AV7). Both electrodes were characterized by linear voltammetry and the production of hydroxyl radicals ((OH)-O-center dot) at their surfaces was assessed by spin trap experiment using N, N-dimethyl-p-nitrosoaniline (RNO) as a spin trap molecule. Slightly higher O-2 evolution reaction (OER) potential was observed with Nb/BDD compared to Si/BDD in both 0.05 M Na2SO4 and AV7 solutions. Enhanced bleaching of RNO was always observed when an increased current density was applied and a significant decay of the adsorption band of RNO was attained with Nb/BDD compared to Si/BDD electrode, indicating higher generation of (OH)-O-center dot on its surface. Complete decolorization of 200 mg L-1 of AV7 was achieved with either electrodes at current density of 30 and 60 mA cm(-2) in 120 min or less. Quite similar degradation efficiency was attained at both electrodes but Si/BDD showed better results than Nb/BDD. Nevertheless, lower energy requirements was achieved by Nb/BDD, demonstrating that it can be a suitable electrode for an efficient electrochemical oxidation process. (C) 2018 The Electrochemical Society.