•MiR-142 levels were significantly increased in the amygdala of rats subjected to SPS.•Npas4 was identified as a direct target of miR-142.•Activation of miR-142 reduced the expression of Npas4 and BDNF.•Administration of LV-anti-miR-142 into amygdalae abolished the behavioral responses caused by SPS. Posttraumatic stress disorder (PTSD) is a prevalent mental disorder that is classified as a trauma- and stressor-related disorder. While numerous epigenetic factors are related to the risk for PTSD, the precise mechanisms underlying this disorder remain unclear. However, accumulating evidence has demonstrated that dysregulation of microRNAs is involved in stress-related psychiatric disorders, resulting in anxiety-like behavior, memory-related deficits and aberrant neuronal plasticity. Here, rats exposed to single prolonged stress showed increased microRNA-142-5p levels in the amygdala and a concurrent reduction in the levels of its predicted target Npas4, an activity-regulated transcription factor, which was implicated in stress-related psychopathologies. In addition, the inhibition of microRNA-142 following exposure to single prolonged stress exhibited decreased anxiety-like behaviors and memory deficits, as well as increased expression of Npas4 and BDNF. Furthermore, a dual-luciferase reporter assay indicated that Npas4 was a direct downstream target of miR-142. Taken together, these data suggest that miR-142 may play a key role in the pathogenesis of stress-related psychiatric disorders.