Ketamine is a commonly used pediatric anesthetic, but it might affect development, or even induce neurotoxicity in the neonatal brain. We have used an in vivo neonatal mouse model to induce ketamine‐related neurotoxicity in the hippocampus, and found that miR‐34c, a microRNA associated with pathogenesis of Alzheimer's disease, was significantly upregulated during ketamine‐induced hippocampal neurodegeneration. Functional assay of silencing miR‐34c demonstrated that downregulation of miR‐34c activated PKC‐ERK pathway, upregulated anti‐apoptotic protein BCL2, and ameliorated ketamine‐induced apoptosis in the hippocampus. Cognitive examination with the Morris water maze test showed that ketamine‐induced memory impairment was significantly improved by miR‐34c downregulation. Thus, miR‐34c is important in regulating ketamine‐induced neurotoxicity in hippocampus.