Nowadays bats fid their shelters more often in the cities, especially in housing estates. Species such as Nyctalus noctula, Vespertilio murinus, Hypsugo savii, Eptesicus serotinus, Pipistrellus pipistrellus, P. nathusii, P. pygmaeus and P. kuhlii are the most common in various crevices and cavities in blocks of flts. Research of bats in Bratislava city shown that the highest amount of species in buildings was found in districts Staré Mesto, Petržalka, Nové Mesto, Ružinov and Karlova Ves. To the main factors which negatively inflence bats in prefabricated houses belong reconstructions, especially related to insulation. All our bat species are protected by law and therefore before and during reconstruction of building it is necessary to make various measures designed to protect them. In the case of destruction of their hiding places in buildings, there is a possibility to put special bat-boxes directly into the insulation, which perform the function of alternative shelters for bats in urban areas.