The thymosinβ(Tβ)gene was cloned from the carp peripheral blood leucocytes by fluorescence differential display reverse transcriptase chain reaction(fluoroDDRT-PCR).The full-length thymosinβ cDNA was 528 bp with the open reading frame located from 40 bp to 178 bp,encoding 46 amino acid residues.Its 5′untranslated region(UTR)is 39 bp and 3′ UTR is 348 bp which contains poly(A)signal(AATAAA)and poly(A)tail.Its GenBank Accession Number is AY457946.The deduced amino acid sequences of the carp Tβ possessed 84%,84%,and 84% similarity with the Tβ a of Cyprinus carpio,Tβ a of Danio rerio and beta thymosin-like protein 2 of Danio rerio.The carp Tβ were clustered with Tβ a of Cyprinus carpio,Tβ a of Danio rerio,Tβ a of Esox lucius,Tβ a of Salmo salar and beta thymosin-like protein 2 of Danio rerio.It is essential for a complete understanding of the mechanisms of thymosinβ in immune response of fish.