Cu-Ga-S ternary thin films were produced by one-step co-electrochemical deposition from an aqueous deposition bath consisting CuCl2, GaCl3 and Na2S2O3 as precursor, and LiCl. The pH of the deposition solution was adjusted to 2.0 adding HCl. Cyclic voltammogram studies were performed in detail prior to the film growth. The best deposition potential was determined to be -0.4 V from the standpoint of the film homogeneity, doping all elements in the bath and avoidance of the immediate atomic aggregation. The chronoamperometry technique was applied to the deposition solution at -0.4 V for 30 min. The effect of Ga content on the film characteristics was investigated. Optical band gap of the films was found to be in 1.6-2.2 eV range. It was concluded that energy band gap of the thin films decreased, as Ga content increased. All deposited films exhibited p-type semiconductor behavior.