Aquatic organisms present, not only simple sources of accumulated metal, but can interact with metals, altering their toxicity. Due to exposition of biosphere with metals, organisms have developed various defense mechanisms to protect themselves against adverse effects of these ions and their compounds.MT is one of that which represent a critical mechanismfor detoxificationof metals.The Sterlet (Acipenser ruthenus) is a bottom-feeding sturgeon specie and because the fish are dependent on invertebrate species for food throughout their life cycle, the Sterlet could be a good indicator of the quality state of water ecosystem. Addition of copper to water leads to the induction of metallothionein. The present study analyzed metallothionein gen that (MT) excreted from liver of Sterlet (Acipenser ruthenus) exposed to sub-lethal copper concentrations (0.075mgL(-1).To begin to elucidate molecular mechanism(s) of sensitivity of sturgeons to metals  a RNA encoding metallothionein (MT) was purified from livers of Sterlet then a cdna was synthetized and the MTgene was amplified. The primary structure of Sterlet metallothionein (S-MT) contained 20 cysteine residues, which is the same as MTs of teleost fishes. However, the primary structure of Sterlet metallothionein contained 63 amino acids, which is longer than any MT identified in teleost fishes but similar to Lake sturgeon and White sturgeon. The complete nucleotide sequence of the Sterlet metallothionein gene has been detected. We have determined the structure of the fish copper-binding protein by DNA sequence analysis of the gene.