This research is making photodetectors with zinc tin oxide (ZTO). By measuring the induced current for analysis and discussion, we found that the photodetectors made of ZTO thin film with an argon-oxygen ratio of 48:2 have maximum photo responsivity of 5.608ሺ𝑚𝐴/𝑊ሻ, and when the annealing temperature is 300℃ for 30 minutes, the photo responsivity exhibited is relatively stable ሺ0~2𝑚𝐴/𝑊ሻ. It proved that annealing can effectively eliminate oxygen vacancies so that the oxygen concentration will no longer cause excessive differences. In addition, the wavelength of the photocurrent used in this research is 380nm , which belongs to the ultraviolet region. Therefore, this research result has the possibility of making ultraviolet photodetectors (UV PD).