Abstract: In summer of 1997, the outdoors living ants of Vienna (the whole district inc1uding urban, suburb an and natural areas) were investigated. Nine different methods were used to sampie 69 sites, and all sites were characterized by measuring eleven ecological parameters. 57 species were identified. Additional informa­tion (e.g. museum collections, literature) resulted in a total of 67 species. The pitfall traps combined with hand collecting proved to be sufficient for obtaining a temporary list of the species of Vienna. Neverthe­ less, the other methods added information on the distribution of several species. There was a tendency of high species numbers at natural, xerothermic sites. The results of simple linear regressions between the number of ant species and the measured parameters showed a positive influence of dryness. The COl1stancy of occurence is differing between the species. According to their distribution patterns some species (e.g. Lasius niger, Solenopsis fugax) cope weIl with urbanization. Some can be c1assified as hemerophile, others as hemerophobe. The results of multiple logistic regressions between the occurence of 37 species and various parameters are used to discuss their autecological requirements. The species composition of the forest sites was c1early defined by c1usteranalysis and showed distinct difference to the other investi­gation sites. Compared to other Central European cities (Linz, Warsaw, Mainz, Köln) Vienna has the most diverse ant fauna. This may be among others a result of its location, overlapping two zoogeographi­ cal zones (Pannonic / Montanic).