The Tasmanian devil is threatened with extinction due to the emergence of a contagious cancer called Devil Facial Tumour Disease (DFTD). Tasmanian devils under 18 months old do not get DFTD. It is possible that genes of the innate immune system may play a role in protecting juveniles and therefore the characterization of these genes is important. Defensins are a small antimicrobial peptide family that displays a wide range of antimicrobial and immunoregulatory functions in a diverse range of species. Known as one of the natural antibiotics of the body this gene family displays extraordinary sequence and bioactivity diversity, reflecting the selection pressures and specific microbial challenges that individual species have faced over millennia. With the recent sequencing of the Tasmanian devil genome it is now possible to characterize the defensin gene family. Using genome and transcriptome mining and hidden markov models we have identified 34 beta defensins and 5 alpha defensins in the Tasmanian devil genome. Each of these genes have similar characteristics to defensins found in other mammals, including a six cysteine motif in the mature peptide, cationic charge (between 1+ to 11+) and high proportion of hydrophobic residues (>30 %). These genes show conservation across mammalian species, as well as species specific gene expansions. Preliminary analysis suggests at least one defensin is widely expressed in the heart, kidney, liver, lung, uterus, blood, lymph node and in primary tumour tissue. Several other defensins show tissue specific expression in the testis and brain. This work provides the first steps for understanding the role of these peptides in the Tasmanian devil and DFTD.