The　multilevel　properties　of　a　memristor　are　significant　for　applications　in　non-volatile　multi-state　storage　and　electronic　synapses.　However,　the　reproducibility　and　stability　of　the　intermediate　resistance　states　are　still　challenging.　A　stacked　HfOx/ZnO　bilayer　embedded　with　copper　nanoparticles　was　thus　proposed　to　investigate　its　multilevel　properties　and　to　emulate　synaptic　plasticity.　The　proposed　memristor　operated　at　the　microampere　level,　which　was　ascribed　to　the　barrier　at　the　HfOx/ZnO　interface　suppressing　the　operational　current.　Compared　with　the　stacked　HfOx/ZnO　bilayer　without　nanoparticles,　the　proposed　memristor　had　a　larger　ON/OFF　resistance　ratio　(~330),　smaller　operational　voltages　(absolute　value　＜　3.5　V)　and　improved　cycle-to-cycle　reproducibility.　The　proposed　memristor　also　exhibited　four　reproducible　non-volatile　resistance　states,　which　were　stable　and　well　retained　for　at　least　~1　year　at　85　°C　(or　~10　years　at　70　°C),　while　for　the　HfOx/ZnO　bilayer　without　copper　nanoparticles,　the　minimum　retention　time　of　its　multiple　resistance　states　was　~9　days　at　85　°C　(or　~67　days　at　70　°C).　Additionally,　the　proposed　memristor　was　capable　of　implementing　short-term　and　long-term　synaptic　plasticities.　©　2022　by　the　authors.