The aim of our study was to assess the seasonal and overnight changes in the flight activity and habitat use of four bat species under the conditions of a sub-mountain town by a detector monitoring. The urban habitats visited from May untill October 1998 – 2000 were divided into three categories: gardens (illuminated or non-illuminated gardens and larger groups of trees), urban habitat (old and new buildings in suburbs and downtown), and water (streams and ponds). Only for Myotis daubentonii was a statistically significant increase in flight activity recorded between the lactation and post-lactation periods. The highest activity of M. daubentonii was recorded in the vicinity of water bodies. The activities of Pipistrellus pipistrellus and Nyctalus noctula were similar in relation to the habitats. Only in Eptesicus serotinus was the activity recorded per habitat type not significantly different. The changes of activity of P. pipistrellus had a bimodal character with the first peak in the 5th and the 6th ten-minutes and the second in the 12th ten-minutes. In N. noctula, activity was characterized by commuting over the urban habitats during the first 0.5 h. Relatively high activity was recorded in E. serotinus during the first 0.5 h in gardens.