AlOx-based resistive switching device (RRAM) with multi-level storage capability was investigated for the potential to serve as an electronic synapse device. The Ti/AlOx/TiN memory stack with memory size 0.48umx0.48um was fabricated; the resistive layer AlOx was deposited using atomic-layer- deposition (ALD) method. Multi-level resistance states were obtained by varying the compliance current levels or the applied voltage amplitudes during pulse cycling. These resistance states are thermally stable for over 1E5s at 125oC. The memory cell resistance can be continuously increased or decreased from each pulse cycle to pulse cycle. More than 1E5 endurance cycles and reading cycles were demonstrated. We further study the potential using this AlOx-based RRAM as electronic synapse device. Around 1% resistance change per pulse cycling was achieved and a plasticity learning rule pulse scheme was proposed to implement the memory device in large-scale hardware neuromorphic computing system.