Abstract: Leptin is the product of ob gene and a kind of Type I cytokine. It is primarily synthesized and secreted by adipocytes and plays an important role in the regulation of ingestion, energy metabolism, skeletal development, thyroid function, and reproduction in mammals. To date leptin gene has been cloned in various teleostean groups, and there have been studies of the physiological functions of leptin. Previous reports have suggested that fish leptin is mainly synthesized in liver, and the amino acid sequence is different from that in mammals; however, the protein structure is highly conservative. Because of its crucial roles in ingestion, glucose and lipid metabolism, and reproduction, Leptin is potentially a new drug target for improving the glucose utilization efficiency in fish in the future. Therefore in this review we discussed about fish leptin in terms of its structure, expression, functions, tissue-specific distribution and receptors.