i conducted a small mammal trapping study in the central paraguayan chaco region of south america to investigate habitat selection by small mammals at different spatial scales. small mammals were collected in forest, successional thorn scrub, pasture, and crop fields representing both relatively undisturbed habitats and agroecosystems. a total of 1089 small mammals representing 13 species were captured during 23 296 trap nights. pastures had the highest species richness as well as the highest number of captures. some small mammal species such as calomys laucha and akodon toba were captured in a variety of habitats whereas others like holochilus chacarius and bolomys lasiurus were captured almost exclusively in pastures. principal components analysis distinguished small mammal species primarily associated with agricultural habitats (e.g. calomys spp.) from those associated with more wooded habitats (e.g. graomys griseoflavus and oligoryzomys chacoensis). these results corroborate other studies on habitat use by small mammals in this region, but with some notable exceptions, such as the first documentation of high densities of calomys musculinus in western paraguay.