Fragile X syndrome, one of the most common forms of inherited mental retardation, is caused by the functional loss of fragile X mental retardation protein (FMRP). MicroRNAs (miRNAs), a newly discovered class of small noncoding RNAs, have been implicated in multiple biological processes through posttranscriptional gene regulation. Recent evidence supports this view in terms of the biochemical and genetic interaction found between FMRP and the miRNA pathway, providing deeper insight into the molecular pathogenesis of mental retardation. This review briefly summarizes the progress towards an understanding of the role miRNAs play in neurological disorders, with a focus on the mechanism of interaction between FMRP and the miRNA pathway in the context of fragile X syndrome. In addition, we go on to discuss how the miRNA pathway may be involved in mental retardation.