The effect of supporting electrolytes in electrochemically-assisted photodegradation process has been investigated on an azo dye, methyl orange. The electrodes used were prepared by sol-gel dip-coating method. Several common inorganic salts were chosen to act as supporting electrolytes, which was added into the dye solution. The anions consist of SO42-, CO32-, NO3- and Cl- while cations were Na+, K+, Ca2+, NH4+ and Mg2+. Linear Sweep Voltammetry was employed to study the photoelectrochemical behaviour of methyl orange solution containing the supporting electrolyte. The presence of certain ions showed pronounced effect towards the rate of photoelectrochemical degradation. The addition of the sodium chloride solution is found to buffer the level of hydrogen ion activity in the solution. © 2004 Elsevier B.V. All rights reserved.