Ga-Sn-O (GTO) thin-film memristor has been developed, and an analog plasticity characteristic has been observed. First, GTO thin-film memristors are fabricated by depositing three GTO layers in a stacked structure using sputtering. Next, the current-voltage characteristics are measured by varying the maximum applied voltage after a certain negative voltage, the hysteresis is observed, and the switching characteristics are evaluated, which is regarded as that an analog plasticity characteristic is observed. The parametric study is done for the stacked structure and deposition process, and the proposed operating mechanism is that oxygen vacancies reciprocate by applying negative and positive voltages. Finally, the pulse application characteristic shows the long-term potentiation and depression, which presents a practical possibility to utilize the GTO thin-film memristor for neuromorphic systems.