In this paper, an atomic layer deposited memristor based on Al 2 O 3 /MoO 3 bi-layer structure is reported. Compared with the single layer MoO 3 based device, the bi-layer memristor demonstrates the improved bipolar switching behaviors including better endurance, higher ON/OFF ratio, and higher uniformity of the programming voltages. Space-charge-limited current (SCLC) model is used to explain the current conduction in our memristor. The formation and rupture of conductive oxygen vacancy-based filaments are illustrated as the proposed mechanism for the observed resistive switching behavior.