Hemolymph was collected from P.vannamei.The total RNA harvested from the hemocyte sample was used to amplify the sequence encoding an open reading frame for mature peptide of penaeidin-2 by RT-PCR.The sequence was cloned into pGEM-T vector and subjected to DNA sequence analysis.The DNA of penaeidin-2 was isolated from pGEM-T/Pen and was cloned into pET-32a（+） expression vector to allow expression of Pen-24 as a fusion protein in E.coli Origami B（DE3）pLys

S

.The fusion protein could be purified effectively by His-Band resin chelating chromatography.The antibacterial activities of Pen-24 was studied by scrip diffusion analysis and the liquid growth inhibition assays. SDS-PAGE revealed the molecular weight of Pen-24 is 24.1×10

3

.The antibacterial activity revealed that Pen-24 displayed antibacterial activity against Gram-positive

Gram-negative bacteria and E.coli against ampicillin and 1 μg Pen-24 fusion protein had identical antibacterial activity with 5 U ampicillin.