We studied the occurrence of bats in urban parks in the city of Madrid (Spain), and the resulting patterns were compared with bat occurrence in the surrounding region. In this way, we addressed if the presence of individual species in the study parks was positively related to their regional occurrence and the way some geographical and environmental traits affected bat richness and composition in urban parks. We analysed urban parks varying in area, structure and distance to the edge of the town. During two years, bats occurring in parks were sampled using ultrasound detectors. A similar sampling method was carried out for four years in the countryside around the city to detect the regional pool of species. The results show that the occurrence of individual species in urban parks was a reduced sample of the regional pool of species and that there was a positive relationship between the occurrence of species in urban parks and the surrounding countryside. This pattern suggests that the more distributed bats at a regional scale were the most frequent ones in parks within the urban matrix. Park area was the main determinant of bat richness. In addition, bat richness distribution reported a nested pattern of species loss as park area decreased. This suggests that bat occurrence in the study parks can be interpreted as the results of a passive sampling of individual species occurring at the regional scale, and that park size was the main determinant of the species occurrence. We conclude that more proactive approaches to bat conservation could be carried out in order to improve the presence of some rare species in urban parks.