Seasonal population characteristics of house mice (Mus musculus), including the effect of season on body mass, were studied at Innes National Park, southern Yorke Peninsula. Mice were caught with Elliott traps, ear-notched, and released. Over 1550 trap-nights (January to December 2006, excluding May), 202 mice were caught. The overall capture success rate was 13.03 mice per 100 trap-nights. The recapture rate was 42.57%. Body mass of adult house mice varied significantly among seasons (P = 0.009). In particular, mouse body mass varied between autumn and winter (P = 0.018), and spring and winter (P = 0.023). The body mass of mice captured in autumn and then recaptured in winter was also significantly different (P = 0.006). This study is the first published for M. musculus population characteristics on Yorke Peninsula and adds to the relatively limited information available on house mouse populations in non-agricultural habitats.