MicroRNAs (miRNAs) are endogenous and non-coding single-stranded RNAs of ~22 nucleotides, many of which are evolutionarily conserved. MiRNAs could orchestrate neuronal development and plasticity by modulating complex gene networks. The perturbation of miRNA expression could potentially contribute to the etiology of human diseases. Over the last 20 years, we have revealed the role of miRNAs in neuropsychiatric disorders, including fragile X syndrome, Rett syndrome, autism and schizophrenia.