<p>The biology of an animal is strongly affected by its body mass, which in turn can influence many aspects of its life history, ecological habits, and morphological diversity. In bats, body mass is a critical element, as it influences aerodynamic variables and echolocation parameters. However, little is known about how body mass impacts the postcranium of bats and its relationship with functional adaptations and ecological traits. Taking this into account, we investigated the relationships between body mass and limb morphological diversity in an assemblage of bats from northern Argentina that includes species from three Neotropical families (Molossidae, Phyllostomidae, and Vespertilionidae). Our hypothesis is that body mass affects the limb bone morphology and that a combination of phylogenetic history, functional adaptations, and ecological factors contribute to the morphological diversity of bats. We assess 32 linear variables (lengths and diameters) of long bones (humerus, radius, femur, and tibia) in a multivariate context. Our sample includes 222 specimens of 37 species and 23 genera of bats with diverse sizes, wing shapes, and foraging strategies. Our results show that the long bones of the forelimb and hindlimb have negative allometry with respect to body mass. Additionally, the structures of bones (e.g., deltopectoral crest, tubercles, condyles) have non-uniform allometric coefficients, exhibiting a proximal-distal gradient of the values. This pattern provides evidence of noticeable modularity and integration in the appendicular skeleton of bats. We also find a strong effect of phylogeny, implying a great influence of evolutionary history on body mass and bone morphology; however, when analyzing the variables individually and considering the different evolutionary models, ecology also appears to affect certain morphological traits of functional importance.</p>