This study was carried out with the objective of evaluating if the size of forest fragments affects the diversity of bat species. In order to do that, seven fragments were studied in Londrina, Paraná: five small fragments, whose areas varied between 1 and 10 ha; a fragment which is considered medium-sized (Parque Municipal Arthur Thomas - 85,47 ha.); and a large fragment (Parque Estadual Mata dos Godoy - 680 ha.). Thirty three species were collected. Ten species were common to all three types of fragments: Chrotopterus auritus (Peters, 1856), Carollia perspicillata (Linnaeus, 1758), Artibeus fimbriatus Gray, 1838, Artibeus lituratus (Olfers, 1818), Platyrrhinus lineatus (E. Geoffroy, 1810), Pygoderma bilabiatum (Wagner, 1843), Sturnira lilium (E. Geoffroy, 1810), Vampyressa pusilla (Wagner, 1843), Eptesicus brasiliensis (Desmarest, 1819), and Myotis nigricans (Schinz, 1821). Eight species were only found in the large fragment: Noctilio albiventris Desmarest, 1818, Glossophaga soricina (Pallas, 1766), Uroderma bilobatum Peters, 1866, Diaemus youngi (Jentink,1893), Diphylla ecaudata Spix, 1823, Eptesicus furinalis (d'Orbigny, 1847), Histiotus velatus (I. Geoffroy, 1824) and Myotis levis (I. Geoffroy, 1824). Five were only found in the small fragments: Noctilio leporinus (Linnaeus, 1758), Phyllostomus discolor Wagner, 1843, Chiroderma villosum Peters, 1860, Eptesicus sp. e Rogheessa tumida H. Allen, 1866. Chiroderma doriae, which is threatened by extinction, was captured in the large fragment and in one of the small fragments; M. ruber, also threatened by extinction, was captured in the medium-sized and large fragments. We believe that the major cause for the loss of organic diversity is not rational exploitation, but the destruction of habitats, a result of the expansion of irrational human activities.