The electrodeposition mechanism of CuGaSe2 (CGS) thin films on ITO substrates has been investigated using cyclic voltammetry technique. The cyclic voltammetric study was performed in unitary Cu, Ga and Se systems, binary Cu-Se, Ga-Se systems and ternary Cu-Ga-Se system. The electrodeposition metallic Ga from Ga unitary electrolytes is impossible due to its low reduction potential. No reduction peak was found for the reduction of Ga3+ to Ga in the cyclic voltammogram of unitary system. However, in the cyclic voltammogram of ternary Cu-Ga-Se system, reduction peak at -0.6 V was observed with addition of GaCl3. Also, current density of the peak was increased with increasing concentration of GaCl3. It is corresponded to the formation of gallium selenides and/or copper-gallium-selenium compounds. The contents of Ga in the films were significantly changed from -0.4 V to -0.6 V. SEM and XRD analysis also showed that surface morphology and crystalline phase of films were significantly changed with increasing Ga content. (C) 2013 Elsevier B. V. All rights reserved.