In this work, we demonstrated that thermal-annealed (GaIn)2O3 films deposited by sputtering can be used for UV detector applications. X-ray diffractometer measurement shows that the (GaIn)2O3 film annealed at 900 °C possesses the best crystal orientation. All annealed (GaIn)2O3 films have a high transmittance of over 80% in the visible light region measured by a spectrometer. The photoresponse of the (GaIn)2O3 film-based photodetectors was affected by the annealing temperature. A film annealed at 800 °C possesses high photosensitivity (2.5 × 104), high photoresponsivity (16.9 A/W), as well as high detectivity (3.11 × 1011 Hz1/2 W–1) at 5 V bias under 254 nm illumination. The photoresponsivity has been improved through thermal annealing. However, further increasing the annealing temperature from 700 to 1100 °C decreased the photoresponsivity. The decay/rise time reduced obviously after thermal annealing. Both the variation of photoresponsivity and response time should concern with the variation of oxygen vacancies. This work is helpful for the preparation of a (GaIn)2O3-based ultraviolet photodetector and the improvement of its response speed and responsivity.