Given　the　intensive　application　of　nanoscale　zinc　oxide　(ZnO)　materials　in　our　life,　growing　concerns　have　arisen　about　its　unintentional　health　and　environmental　impacts.　In　this　study,　the　neurotoxicity　of　different　sized　ZnO　nanoparticles　in　mouse　neural　stem　cells　(NSCs)　was　investigated.　A　cell　viability　assay　indicated　that　ZnO　nanoparticles　manifested　dose-dependent,　but　no　size-dependent　toxic　effects　on　NSCs.　Apoptotic　cells　were　observed　and　analyzed　by　confocal　microscopy,　transmission　electron　microscopy　examination,　and　flow　cytometry.　All　the　results　support　the　viewpoint　that　the　ZnO　nanoparticle　toxicity　comes　from　the　dissolved　Zn2+　in　the　culture　medium　or　inside　cells.　Our　results　highlight　the　need　for　caution　during　the　use　and　disposal　of　ZnO　manufactured　nanomaterials　to　prevent　the　unintended　environmental　and　health　impacts.