Transferrin of f ish sera is a kind of non..heme ....globulin banding irons in fish sera. Transferrin has not only the property of lower oxygen tolerance but also the property of anti..diseases. Transferrin is coded by only one gene exceeding 10kb in size and it s gene has much repetition structure. The two pairs of primers P1, P4 and P2, P3 were designed and synthesized according to the banding and functional sites of irons while referring to published cDNA or gene sequences of f ish transferrins in the Database of GenBank. The reaction conditions of PCR are: fore.. denaturation, 96 .. , 4min; denaturation, 96 .. , 1min; annealing, 60 .. , 1min; extension, 72 .. , 2min; cycle number, 35; last extension, 72 .. , 10min. The pGEM..T vector system was used in cloning process. An 866bp length key segment sequence of crucian carp serum transferrin cDNA was cloned. Another two pairs of primers P5, P6 and P7, P8 were designed and synthesized according to the key segment sequence respectively. 5.. end ( 787 bp) , 3.. end ( 1081bp) and the full..length cDNA of crucian carp serum transferrin cDNA were cloned by RACE respectively. The full..length cDNA ( 2444 bp) of crucian carp serum transferrin cDNA was arranged in computer. The deduced protein sequence length is probably 807bp. The homology of cDNA sequences of 14 f ish serum transferrins was compared. Their homology is between 30% and 80%. The result shows that Cyprinidae fish ( such as Carassius auratus , C. gibelio, Cyprinus carpio, and Danio rerio ) has very close relat ive relationship. Their homology is more than 50% . At the same t ime, phylogenetic evolution was also analyzed. The evolut ional conservatism and amino acid sequence homology of fish serum transferrins were conf irmed. DNA Club, DNAman v4. 0, DNA Tool v5. 1 and BLAST v2. 0 were adopted in the process of nucleotide sequence analysis. The nucleotide sequence analysis offers even more direct evidence for the hypothesis that recent transferrin is from original transferrin banding single iron site, deriving from common ancestor of 5 .. 109 year ago and forming many branches of homology transferrins and homology analogs in different animals and different cells or tissues during a long evolutional process. Furthermore, the analogy of transferrin structure and function f rom different resources are based on the analogy of transferrin genes.