AbstractMicroorganisms are an important group of organism mainly performing catabolic metabolism, which display extreme abundance in biodiversity. However, due to their microscopic sizes, especially prokaryotes with simple unicellular structure, their asexual propagation, their rapid replication and the lack of base line inventory of their groups and quantity, the biodiversity of microorganisms has so far not been studied thoroughly and has been paid little attention compared with macro organisms. In the present paper, the biodiversity of microorganisms is reviewed briefly, with consideration of the following aspects: species diversity, diversity of phylogenetic lines, physiological diversity and genetic diversity. The aim is to improve awareness of investigation of microorganism resources, not only in the scientific community but also in society as a whole.