The conduction mechanism and resistive switching properties in a resistive-random-access-memory device composed of Al(top)/TiOx/TiO2/Al(bottom) are investigated in this paper. The active-top-electrode (TE) material aluminum interacted with the TiO2 layer and induced an oxygen-deficient TiOx layer near the TE. The naturally formed oxygen-deficient TiOx layer was confirmed by a transmission-electron-microscope energy-dispersive X-ray spectrometry analysis. The oxygen-deficient TiOx region acted as a trap for electrons and contributed to the resistive switching. The proposed mechanism and measured data are verified through simulation of a two-variable resistor model.