The Tasmanian devil (Sarcophilus harrisii) is the largest remaining carnivorous marsupial. The future of the Tasmanian devil is under threat from a contagious cancer, Devil Facial Tumour Disease (DFTD), which has already decimated over 85% of the population. Interestingly, young devils do not catch DFTD, and we hypothesize that antimicrobial peptides within the mother’s milk may protect the young against infection. Cathelicidins are a family of antimicrobial peptides within mammals which contribute to innate immunity through antimicrobial and immunomodulatory functions. They have been studied extensively in eutherian mammals but marsupials are relatively unexplored. Marsupials have a short gestation period and give birth to altricial young which are immunologically naive. During development the young are protected from microbial infection by cathelicidins expressed in the mother’s milk, pouch epithelium and skin of the young themselves. This unique reproductive physiology has encouraged lineage specific expansion of the cathelicidin gene family within marsupials, resulting in numerous diverse peptides. We identified six cathelicidins in the Tasmanian devil genome and have synthesized the mature peptides. These will be tested against a range of pathogens, including DFTD cells. Thus far only bacteria and fungi have been tested, with promising results. One cathelicidin was more effective at killing Cryptococcus gattii and Cryptococcus neoformans than the antifungal drug fluconazole. Furthermore, two cathelicidins were capable of killing methicillin-resistant Staphylococcus aureus, vancomycin resistant Enterococci and numerous human clinical isolates. Cytotoxic and haemolytic activity of all cathelicidins against human cells has also been determined and only two are moderately toxic. This study highlights the potential for marsupials such as the Tasmanian devil to provide new drugs to treat human and animal disease.