Abstract:The occurrence of Rhogeessa hussoni Genoways and Baker, 1996 in the state of Sergipe is reported here based on an adult female collected in mist nets during a chiropteran survey of the Refúgio da Vida Silvestre Mata do Junco (RVSMata do Junco), a 894 ha fragment of lowland Atlantic Forest. Measurements and taxonomic comments about this species are given. Despite the variability found in coloration of the ventral pelage, qualitative and quantitative characters allowed the identification of the specimen as R. hussoni. The present record increases to twenty-eight the number of bat species recorded for Sergipe and confirms the presence of R. hussoni in the Atlantic Forest biome. The genus Rhogeessa H. Allen, 1866 consists of ten Neotropical species and ranges from Tamaulipas, in Mexico, to southeastern Brazil (Goodwin 1958;Nowak 1994;Peracchi et al. 2011). Specimens of this genus are rare in zoological collections, probably due to the difficulty of capturing vespertilionids in mist nets set at ground level, the most used sampling method in bat inventories. Therefore, there is a relative paucity of published data on geographical distribution and taxonomy for this genus (Aires et al. 2011). The two species of the genus found in Brazil are Rhogeessa hussoni Genoways and Baker, 1996 and Rhogeessa io Thomas, 1903(Simmons 2005Peracchi et. al. 2011).Rhogeessa io is known in Brazil from the states of Amazonas, Maranhão, Mato Grosso, Paraíba, Paraná, and Pernambuco (Percequillo et al. 2007; Bickham and Ruedas 2008; Aires et al. 2011;Peracchi et al. 2011). Rhogeessa hussoni occurs in southern Suriname and Brazil (Simmons 2005), where there are records from the states of Bahia, Maranhão, Mato Grosso, Minas Gerais, Pará, Paraíba, Pernambuco, and Paraná (Aires et al. 2011;Peracchi et al. 2011). These bats are small in size, with a diet consisting exclusively of airborne insects (Wilson 1973). In spite of the paucity of mensural data available for R. hussoni and R. io, differentiation between these species has been based mainly on size, with R. hussoni being larger than R. io (Genoways and Baker 1996, Bickham and Ruedas 2008).During a bat survey at the Refúgio da Vida Silvestre Mata do Junco (RVS-Mata do Junco) (10°32' S, 37°03' W), a 894 ha state reserve located in the municipality of Capela, 86 km from Aracaju, the capital of the state of Sergipe, in northeastern Brazil (Figure 1 It is a fluid-preserved specimen, with skull removed. External and cranial measurements of this specimen were obtained with the aid of caliper precise to 0.02 mm and following criteria described by Taddei et al. (1998) Measurements obtained for the metacarpals of the specimen ALP 9656 are above the range described for R. io and closer to the values reported for R. hussoni. Forearm and cranial measurements also agree well with the values reported by Genoways and Baker (1996) for R. hussoni, being generally larger than those of R. io (Table 1). The lower toothrow length, which is known to be larger in R. io, is within the range reported for...