Habitats associated with oak may host high insect diversity, especially saproxylic species, due to the availability of specific microhabitats such as dead wood, rotten logs and woody debris. Among the insects occurring in such habitats, ants play a major role in forest ecosystems as generalist predators. Ant assemblages were investigated using different types of traps. Sampling was carried out in 2015 and 2016, in a wood-pasture located in eastern Transylvania (Romania). Differences between species richness and composition in different types of oak habitats were tested: solitary oak in pasture, oak stand, and the ecotone separating them. Altogether a total of 17 ant species were identified. The three habitats shared an important proportion of the species, yet significant differences between the three habitats in terms of community composition were found. The highest diversity of ant species was recorded in the oak stands, followed by the solitary trees, though differences were not significant. Oak associated habitats can sustain high diversity of ant species and moreover thermophilic specialists thrive. Finally, the abundance of Lasius brunneus is highlighted, the species being proposed as a wood-pasture specialist.