We report the effect of the oxygen content of the LaAlO3 layer on the synaptic behavior in the Pt/LaAlO3/Nb-doped SrTiO3 memristor for neuromorphic applications. As the oxygen-content decreases, the current becomes larger and the spike time-dependent plasticity (STDP) becomes less sensitive to the time difference between preand post-synaptic spike voltage. In addition, the conduction mechanism, which was found to be a combination of thermionic and Poole-Frenkel emissions, and the effect of oxygen content are explained in association with the oxygen vacancy in the LaAlO3 layer. The trade-off between large current and efficient STDP can be controlled by the oxygen content. Furthermore, the results of extracting the synaptic strength-based model parameters indicate that the Pt/LaAlO3/Nb-doped SrTiO3 shows the efficient STDP characteristics in comparison to previously reported memristor materials.