In the present work, amorphous Ga₂O₃ (a-Ga₂O₃) thin films have been developed on both flexible polyimide(PI), rigid quartz glass and Si substrates via using radio frequency magnetron sputtering at room temperature. The effect of oxygen/Ar flow rate ratio on the structural, optical, surface morphology as well as chemical bonding properties of the a-Ga₂O₃ films was systematically investigated and elucidated. The average optical transmittance of the a-Ga₂O₃ films is over 80% from 300 to 2000 nm. The extracted optical band gap of the a-Ga₂O₃ films increases from 4.97 to 5.13 eV with increasing O₂/Ar flow rate ratio from 0 to 0.25, resulting from a suppression of oxygen vacancy defects as increasing O₂ partial pressure during growth. Furthermore, the optical refractive index and surface roughness of the a-Ga₂O₃ films have been optimized while the O₂/Ar