Abstract: Transferrin has diverse functions that not only participates in the transportation and metabolism of organism iron ions,but also plays key effect in cellular respiration,cellular growth and proliferation,moreover,it has the antimicrobial bactericidal bioactivity.This study screened and cloned Ctenopharyngodon idellus transferrin gene(CtTf) from grass carp cDNA library.This full CtTf sequence was 2322bp and contained a 5'untranslated region of 31bp and a 3'untranslated region of 266bp.The CtTf ORF contained 2025bp which could code a 674 amino acids peptide.Forecasting molecular characteristics of this CtTf by the online software,the result showed that N-lobe of grass carp transferrin was a signal peptide of 15 amino acides.This gene was composed of two similar domains,and the identity of the two domains was 31%.Similarly with the transferrin in other animals,grass carp transferrin has four iron ion binding sites in each domain,and positions of them were relatively conservative.There were several other conservative sites besides the eight iron ion binding sites in the domains.Grass carp transferrin had the high homology with human and other species,such as it shared the identity of about 65%-73% with other Cyprinid fish,43%-50% with marine fish,and 40%-42% with amphibians,reptiles,aves and mammals.Phylogenetic tree analysis revealed that grass carp transferrin gene shared the highest homology with zebra fish and cyprinoid.The result of RT-PCR experiment indicted that,among the liver,intestine,kidney,spleen,heart,muscle,gill and brain of grass carp,the transferrin gene had the highest expressional level in liver,the spleen and intestine ranked secondly,which had trace amount in gill and brain.