Mycoplasmas cell wall-less bacteria of the class mollicutes, are among the smallest self-replicating organisms known and have been described as minimal living units. The presence of a small genome and the lack of numerous biosynthetic pathways correlate with growth requirements for macromolecular precursors such as phospholipids, cholesterol, amino acids, and nucleotides. Mycoplasma nuclease are thought to play a metabolic role in the production of nucleotide substrates from host or microbial nucleic acids released through natural and induced cell death. Nuclease activity in members of the mollicutes has been proposed as the mechanism by which these organisms acquire the precursors required for their nucleic acids. Nucleases are multifunctional enzymes and widespread in distribution. Intracellularly, they have been implicated in recombination, repair and replication, whereas extracellular enzymes have a role in nutrition. Nucleases are thought to be important contributors to virulence and crucial for the maintenance of a nutritional supply of nucleotides in mycoplasmas that are pathogenic in animals and human. Nucleases detection is a significant findings for an etiologic diagnosis and for determining the virulence of the mycoplasma strain isolated in the laboratory. Because of the importance involving nucleases, presented this review.