Wildfire is a pervasive disturbance in the boreal forest, and fire size and severity is increasing due to climate change. Yet, wildfire impacts on boreal bats are unknown. Burned forest may be attractive to bats because of an increase in dead trees and a reduction in vegetative clutter. Using ultrasonic detectors, I sampled little brown bat (Myotis lucifugus) activity at lakeshore and upland sites within burned and mature forest. Activity was greater in mature than burned forest at both upland and lakeshore sites. Activity was greater at lakeshores, where some large snags survived fire. The relative use of edges created by fire, lakeshores and roads was also investigated. Bat activity was greater at lakeshores than other edge types. Bats made little use of burned upland areas or fire-created edges. This study provides a first approximation of the effect of a ‘megafire’ on bats in the boreal forest and suggests that large, severe wildfires may have a negative impact. Protection of mature forest containing large dead trees, particularly along lakeshores, may help to mitigate the loss of habitat due to wildfires. Further work, however, is needed to assess bat activity in burns of differing sizes, severity and age.