Because of expanding urban areas and subsequent changes in land cover, elucidating the role of preserving biodiversity in heterogeneous urban green spaces in city scapes is necessary. Alpha, beta, and gamma diversity of ant assemblages were analyzed in a heterogeneous urban green space in the highland city of Tlaxcala in central eastern Mexico. Ant and habitat characteristics were sampled during hot and rainy seasons of 2017 in an urban green space divided into nine sections. In total, 842 individuals of 21 species, 12 genera, nine tribes, and four subfamilies were collected. Sections with more complex habitat structure had fewer and more dominant species, whereas those with simple habitat structure had greater number and evenness of species. Compositional diversity varied significantly among the sampled sections because of much species turnover and great contribution of beta diversity to gamma diversity. The value of the studied urban green space for ant diversity resulted from much turnover of species. Promotion of heterogeneity in urban green spaces in city scapes might be an important strategy for conserving biodiversity as well as ecosystem services provided in and near highland cities.