A novel crustin-like antimicrobial peptide (Crus-likePm) was identified from haemocytes of Penaeus monodon. The deduced amino acid sequence of a Crus-likePm consists of 124 amino acid residues of the mature peptide and a signal peptide of 17 amino acid residues. The mature peptide contains a glycine-rich domain at the N-terminus and 12 conserved cysteine residues containing a single WAP domain at the C-terminus. Phylogenetic tree and sequence comparison clearly confirmed a distinct between a Crus-likePm and other shrimp crustins. Genomic organization and upstream region of a Crus-likePm gene was investigated. The gene consisted of two exons and one intron. The 5'-flanking regions of a Crus-likePm gene contain multiple putative transcription factor binding sites. mRNA transcript of a Crus-likePm was found to be abundantly expressed in haemocyte and highly up-regulated after Vibrio harveyi injection. The mature Crus-likePm was cloned into the pET28b with an N-terminal hexa-histidine tag fused in-frame, and expressed in E. coli. The purified recombinant Crus-likePm showed strong antimicrobial activity against both Gram-positive and Gram-negative bacteria including V. harveyi, a major pathogenic bacteria in shrimp aquaculture.