Abstract: Hemolyph was collected from Scylla paramamosain. The total RNA extracted from the hemocyte sample was used to amplify the sequence encoding an open reading frame of a mature peptide of CrusSp by RT-PCR. The sequence was cloned into pMD18-T vector and subjected to DNA sequence analysis. The DNA of CrusSp was isolated from pMD18-T/CrusSp and was cloned into pET-32a(+) expression vector to allow expression of CrusSp as a fusion protein in E. coli OrigamiTM (DE3). The fusion protein could be purified effectively by His-Band resin chelating chromatography. The antimicrobial activities of CrusSp were studied by agar diffusion test. Analysis by 15% SDS-PAGE revealed that the molecular mass of CrusSp is 10.27 kDa. The antimicrobial activity revealed that CrusSp exhibited antifungal activity towards Trichoderma viride.