The effect of sputtering power on the amorphous Ga2O3 thin film deposited using the radio frequency sputtering system was evaluated. Amorphous Ga2O3 is cheaper and more efficiently fabricated than crystalline Ga2O3, and is studied in various fields such as RRAM, photodetector, and flexible devices. In this study, amorphous Ga2O3 was deposited by radio frequency sputtering system and represented a transmittance of over 80% in the visible light region and a homogeneous and dense surface. The optical band gap energy decreased as the sputtering power increased owing to the quantum size effect. Thus, the specific band gap of amorphous Ga2O3 can be obtained by adjusting the sputtering power, it indicates amorphous Ga2O3 can be used in various fields.