Abstract:As an important complement of the information obtained from mtDNA, the internal transcribed spacer (ITS) of nuclear ribosomal DNA is being increasingly applied in entomological study. This paper introduced the structure and characters of ITS, and summarized its applications in identifying insect species and in studying their relative relationships and phylogenesis, evolution and spread, and relations with environment. ITS was mainly applied in identifying the species whose morphological differences were subtle. The research of relative relationships and phylogenesis was aimed to understand the species origin and evolution, while the study on the relations with environment was mainly focused on sociological and parasitic insects. The problems and their possible causes in ITS application were discussed.