Human β-defensin-2 (hBD2) is a small antimicrobial peptide with potential as a therapeutic agent. The effect of codon usage on the expression of hBD2 in Escherichia coli was studied. Two coding sequences encoding the same hBD2 precursor were both expressed as fusion protein with thioredoxin in E. coli BL21 (DE3). One is the wild-type human cDNA and the other is a gene synthesized by a PCR-based method in which rare codons were altered to those frequently used in E. coli. The expression level of recombinant hBD2 was over 50% of the total cellular protein when the synthetic gene with preferential codons was employed which was a 9-fold enhancement over the wild-type cDNA. The result shows the codon bias of the host was a major barrier in high-level expression of recombinant hBD2 and suggests a similar approach may be used in the expression of other defensins in E. coli.