The effects of Ga doping on structural, electrical, and optical properties of hydrogenated ZnO-Ga (GZO) thin films deposited by sol-gel technique have been investigated. From the X-ray diffraction observations, the films doped with different gallium concentrations were found to be pure wurtzite-structured ZnO. The electrical properties of the hydrogen-annealed films were improved and a lowest resistivity of 3.410×10-3Ω·cm was obtained. The refractive index and extinction coefficient of ZnO-Ga thin films were determined in the range of 270~1600 nm by varying angle spectroscopic ellipsometry (VASE). The simulation was carried out using a double oscillator model, which includes the Psemi-MO equation and the rho-tau Drude equation.