Interleukin-1beta (IL-1β) plays a significant role in the onset and pathogenesis of inflammation in mammalian hosts. Although well characterized in a range of vertebrate species, little is known about this important cytokine in marsupial mammals. We report here the molecular cloning and characterization of IL-1β in the tammar wallaby (Macropus eugenii). M. eugenii IL-1β has an open-reading frame of 813 nucleotides, coding for a putative protein of 270 amino acids to the termination codon. The IL-1 family motif and potential caspase cleavage site (necessary for production of the mature protein) is also present in the sequence. Molecular characterization of tammar wallaby IL-1β provides fundamental information necessary to progress the study of functional immune responses in this unique group of mammals.