Detailed alien species inventories are important to assess strategies for its management. We built a vascular alien plant specieslist from published papers available for the Río de la Plata grasslands (RPG). Species were described regarding their geographicorigin, life form, photosynthetic pathway (only Poaceae), human use, and invasion status according to legislation of Brazil,Argentina and Uruguay. Occurrence records were obtained from Global Biodiversity Information Facility and rasterized intogrid-cells of 10 arc minutes resolution.The alien flora of the RPG comprises 592 species, among which 317 are considered invasive and 275 naturalized. Alien species canbe sourced to all continents, although most species have their native range from Temperate Asia (n = 413), Africa (n = 382), andEurope (n = 362). Herbs are the most frequent life form (n = 332), followed by graminoids (n = 125) and trees (n = 72). However, 86%of alien tree species are invasive. Regarding invasive species, only 8 species are common to three countries. We registered 235 exclusive invasive species in Argentina, 40 in Brazil and 9 in Uruguay. Alien species richness was higher in areas closer to major cities.Even so, we highlight higher alien species richness in Argentina. There is no clear spatial pattern regarding geographical origin,reflecting favourable conditions for alien species from different ecological contexts in the region. Our results have implicationsfor long-term conservation management of native biodiversity. Efforts to control alien species should surpass political boundariesand encompass all ecological units of the RPG.