The internal transcribed spacer (ITS) of the nuclear ribosomal DNA, as an important complement of information obtained from mtDNA, is being used increasingly to construct or reconstruct phylogenetic relationships among species and to distinguish morphologically similar species in invertebrates. The composition and characteristics of nrDNA ITS were reviewed in this paper. Recent progress in invertebrates phylogenetic studies based on of ITS sequences invertebrates was summarized. Some problems in this field ...