Leptin, the product of the obese gene, is one of the key factors for the regulation of food intake and whole-body energy balance. Both grass carp ( Ctenopharyngodon idellus
) and silver carp ( Hypophthalmichthys molitrix
) leptin full-length cDNA were cloned by RT-PCR and RACE methods. The sequences of leptin cDNA in grass carp and silver carp were 1 096 bp, 1 176 bp, and the deduced protein had 173, 172 amino acids respectively. The amino acid homologues analysis showed high identity in cyprinid fish. Despite lower amino acid identity between cyprinid fish and other leptins, conservation of both cysteine residues that formed leptin’s single disulfide bridge inside the chain presented a certain similarity. Phylogenetic tree showed that leptin in grass carp and silver carp were in the same branch as other fishes. The 5'-flanking region and introns of leptin in grass carp and silver carp were characterized using Genome Walker and PCR methods. The genes were 2 129 bp and 2 192 bp in length respectively in grass carp and silver carp, with similar gene structures in other vertebrates (including 3 exons and 2 introns). This research will be helpful for further studies of fish leptin in cultivation and food safety.