Abstract:Denitrification is carried by a diversity of bacteria belonging taxonomically to the various genus, which precludes the use of 16S rRNA-based routine methods to study denitrifiers. However, as a molecular marker, the functional genes of encoding denitrifying enzyme can be employed to investigate the community structure, abundance and activity of denitrifying bacteria in environmental samples. In this review, we introduced the denitrifying functional genes and their amplifying primers, compared the phylogenetic relationship of the denitrifying functional genes with 16S rRNA genes and community distribution of nirS denitrifiers with nirK denitrifiers. The article also summarized the studies and applications recently of denitrifying functional genes, discussed the problems unresolved in researches, which would be expected to be a reference for studying complex microorganisms.