A 1 438 bp full length cDNA sequence of β-actin gene from Hypriopsis cumingii was obtained with RT-PCR and rapid amplification of cDNA ends(RACE)technique.It consists of a 92 bp 5′ untranslated region(UTR), a 1 134 bp open reading frame(ORF)and a 257 bp 3′UTR.The translated protein is composed of 377 amino acids,with 41.9 ku molecular weight,and its calculated isoelectric point was 5.3.The amino acid sequence of β-actin in H.cumingii has six specific amino acid residues:Met178,Ser305,Ser321,Pro325,Val331 and Pro346,respectively.In addition,three other particular base sites of amino acid residues were found in these sequences.Similarly,two characteristic amino acid residues of some mollusks were obtained.The amino acids sequence of β-actin in H.cumingiishared the high similarity with Molluscs,Arthropod and Vertebrate animals(98%-99%).Neighbor-Joining(NJ)tree suggested that H.cumingii clustered with Mollusca firstly,and then clustered with Arthropoda,finally clustered with Fish,Amphibians,Mammals. Semi-quantitative RT-PCR analyses showed that the expression level of β-actin gene in H.cumingii was stable in eight tissues:mantle,blood,liver,kidney,stomach,gut,gill and abdominal foot.