Because diurnal roosts can be important in determining bat occupancy and abundance in forested habitats, we identified characteristics of cavity trees that influence roost selection by Corynorhinus rafinesquii (Rafinesque's Big-eared Bats) and Myotis austroriparius (Southeastern Myotis) in east Texas. We identified used and non-used cavity trees with a combination of transect searches, radiotelemetry, and historical records at 7 study areas. Both bat species selected similar cavity trees for summer diurnal roosts, showing an affinity for tupelo trees (Nyssa spp.), with 55% of diurnal roosts in Nyssa aquatica (Water Tupelo) and 33% in N. sylvatica (Blackgum). Of 17 tree and habitat variables we measured at used and unused cavity trees, those related to cavity size and availability (cavity height and diameter, tree diameter, density of large trees in the area) were the most important predictors of use. Characteristics of the surrounding stand at both local and landscape scales were less important. Rafinesque's Big-eared Bats and Southeastern Myotis appeared to use the largest cavity trees present and we speculate that the availability of suitable trees with large cavities may limit abundance in this region.