Here we present the first detailed phytosociological description of the plant communities of the Transaltay Gobi, the driest region within Outer Mongolia. It was originally gazetted as a national park by the Mongolian parliament in 1976, which included also the Dzungarian basin in south-western Mongolia. The status of the Great Gobi A National Park in the Transaltay Gobi, and the Great Gobi B National Park in the Dzungarian Gobi was later raised to the level of Strictly Protected Area. Since the area hosts many endangered wildlife species, we offer an initial vegetation description, which is necessary to understand the habitats of this arid ecosystem. Based on a modified Braun-Blanquet approach we designated eight zonal vegetation units, most of which are impoverished regional variants of vegetation types previously described from adjacent regions; most units contain several sub-units. The altitudinal gradient reflects the climatic regime in the study area; therefore the vegetation distribution follows the precipitation gradient regarding both vegetation cover and diversity. The most important diagnostic species are typical drought-adapted central Asian elements, namely Haloxylon ammodendron, Ephedra przewalskii, Reaumuria songarica and Anabasis brevifolia. Three new associations were designated based on our vegetation data. The main determinant for the riparian vegetation types is apparently groundwater availability, leading to locally high soil salt contents due to the high evaporation in the region. Poplar stands, reed beds and Tamarix stands are the characteristic vegetation types of the oases in the working area.