Abstract: Bacterial small RNAs(sRNAs)have been one of the important research subjects in microbiology in last decade. They mainly act as a group of regulators controlling bacterial gene expression at post-transcriptional level. Most sRNAs regulate their mRNA targets involved by Hfq, which can facilitate base-paring of sRNA-mRNA and further affect mRNA stability or translation process. In this work the structure of Hfq, the molecular mechanisms of Hfq in sRNA regulation, and its influences detected in various bacterial species are reviewed. As a small chaperon protein ubiquitously present in many bacteria, the homohexamer form of Hfq possesses two unequivocal facets which can bind different types RNAs and promote their interaction. Such a structure provides a basis for its functional roles in mediating sRNA-mRNA interaction. While the hitherto studies on Hfq are mainly restricted in Gram-negative bacteria, its roles in some Gram-positive bacteria remain elusive. Moreover, the mechanisms underlying the impacts of Hfq on many important bacterial species have been still not clear. In future, it is necessary to further investigate the fine structure of Hfq with regard to its function as well as the detailed mechanism of the diverse bacterial phenotype affected by Hfq.