The SWDPm2 or single WAP domain (SWD)-containing protein isoform 2 from black tiger shrimp Penaeus monodon belongs to type III crustin, which possesses both antimicrobial and anti-proteinase activities. SWDPm2 in shrimp hemocytes was highly up-regulated against Staphylococcus aureus, yellow head virus (YHV) and white spot syndrome virus (WSSV) infection. The recombinant SWDPm2 (rSWDPm2) was expressed in Escherichia coli and purified by Ni Sepharose column. rSWDPm2 predominantly inhibited the growth of Gram-positive bacteria, but not the Gram-negative bacteria. The protein can agglutinate the Gram-positive bacteria and spores of Ecytonucleospora hepatopenaei (EHP) in vitro. Scanning electron microscope revealed the morphological alterations of S. aureus, Vibrio parahemolyticus and spores of EHP when they were incubated with rSWDPm2, suggesting the action of rSWDPm2 against them. In conclusion, SWDPm2 is a potent agent with broad activity.