We investigated electric and chemical properties of metal/Y2O3 interfaces. The Pt/Y2O3 interface can be chemically activated by bias voltage, resulting in a microscopic oxidation-reduction center at interface. The oxidation-reduction of the center alternatively changed resistance of the Pt/Y2O3 system, and the alternation yield hysteresis with respect to the bias voltage, i.e. a memory effect. On the other hand, in Au/Y2O3 system, non-oxidization of Au induced ejection of O2 gas from the interface, so that there was no memory effect. Possible reactions of these metal/Y2O3 systems were proposed, and the balance between oxidation and reduction at microscopic center was concluded to be essential for the memory effect.