Large home range sizes are not unusual for small forest-dwelling bats living in cold temperate climates. However, lesser short-tailed bats (Mystacina tuberculata) feed on the ground for a proportion of their time, so their home range requirements may not conform to predictions based on other bat species. The home range size requirements of a population of M. tuberculata were investigated in cold temperate rainforest in the Eglinton Valley, Fiordland, New Zealand. Home range data was collected from a total of 21 out of 23 radio-tagged bats during late summer to early autumn of 1997 and 1998. Individual bats were followed for an average of 7.8 ± 3.2 (SD) days and collectively ranged over a total area of 14,710 ha. Thirteen colonial roosts were located within a central roosting area occupying 17 ha. A further 10 solitary roosts were located within individual foraging areas. Individual 100% minimum convex polygons varied considerably in size from 127.3 to 6,223.4 ha (median = 478.5 ha) with a range length of 2.2–23.0 km (median = 5.0 km). Cluster analyses revealed individual home ranges contained multi-nuclear patches of activity. Despite their large home ranges, bats concentrated activity (85%) in small core areas of 0.6–270.3 ha (median = 26.5 ha), with 85% of core areas less than 62 ha in size. Moderate levels of home range overlap amongst individuals (median = 26.8%) decreased to low levels for individual core areas (median = 3.7%). Our results show that M. tuberculata have relatively large home ranges, similar to many other small temperate rainforest bats, and implies that conservation areas designed for M. tuberculata should be large. Our predictions should be tested on populations of this species in areas with more abundant resources and milder climates.