Abstract: Arginase (Arg) is a sign enzyme among organisms of urea cycle. It is not only related to many diseases inorganisms, but also used to treat tumors and cancer as an important tool enzyme. According to the Hyriopsis cumingii (H.cumingii) expressed sequence tags (EST) obtained by constructing subtractive hybridization cDNA library of H. cumingiiliver, the gene full-length cDNA sequence of arginase from H. cumingii was cloned by RACE-PCR technique basedon the designed gene-special primers. After analyzed by the software DNA Star and the bioinformatics technology, theresults showed that the length of arginase gene cDNA sequence was 1720 bp, containing a complete open reading frame(651072) which was 1008 bp, encoding a peptide of 335 amino acid residues (aa), flanked by a 64 bp of 5 untranslatedregion (UTR) and a 648 bp of 3-UTR. The deduced molecular weight of arginase was about 36.81 kD. At thetranscriptional level, quantitative real-time PCR (qPCR) was used to detect the expression of the arginase gene indifferent tissues. The result revealed that H. cumingii arginase gene could be expressed in seven kinds of tissue containingliver, stomach, intestine, gill, heart, mantle, axe foot collected from H. cumingii, especially strongly expressedin digestive organs, such as liver, stomach and intestine, but weakly in heart and mantle. So it concluded that thearginase from the H. cumingii which belongs to lower invertebrate could possess the same characteristics and functionsof arginase typeⅠandⅡfrom the higher animals. That means the arginase from the H. cumingii may not onlyparticipates in urea cycle, but also plays an important role in the processes of physiology and pathology. And the deductionwill be verified in the next experiment.