Aims and study area: We present the first formalised large-scale syntaxonomic overview of mesic semi-natural grassland communities (Arrhenatheretalia elatioris and Nardetalia strictae) in the Ukrainian part of the Eastern Carpathians and adjacent areas of Hungary, Slovakia and Poland. Methods: During 2009-2014 we recorded 759 phytosociological releves using the Braun-Blanquet approach. The classification was based on our own phytosociological material as well as published material recorded by both Braun-Blanquet and eco-phytocenotic (dominant) approach comprising 2,000 phytocoenological releves in total (952 releves in the stratified data set). Semi-supervised and supervised classifications by the K-means method and indirect gradient analysis by detrended correspondence analysis were used for the analyses. Slovak electronic expert system and diagnostic species for grassland vegetation published in national overviews in the neighbouring countries helped us to identify individual clusters. Didukh indicator values were used to compare habitat conditions of delimited plant communites. Results: A total of fifteen well-differentiated associations within five alliances and two classes were delimited: Class Molinio-Arrhenatheretea including the alliance Arrhenatherion elatioris with associations Anthoxantho odorati-Agrostietum tenuis, Betonico officinalis-Trifolietum pannonici, Poo-Trisetetum flavescentis, Primulo veris-Agrostietum capillaris and Pastinaco sativae-Arrhenatheretum elatioris and the alliance Cynosurion cristati with associations Plantagini-Lolietum perennis and Lolio perennis-Cynosuretum cristati. Class Nardetea strictae including the alliance Nardo strictae-Agrostion tenuis with associations Antennario dioicaeNardetum strictae, Campanulo abietinae-Nardetum strictae and Betonico officinalis-Agrostietum capillaris, the alliance Violion caninae with associations Campanulo rotundifoliae-Dianthetum deltoidis, Hyperico maculatiDeschampsietum flexuosae, Festuco rupicolae-Nardetum strictae and Polygalo vulgaris-Nardetum strictae caricetosum fuscae and the alliance Potentillo ternatae-Nardion strictae with association Soldanello hungaricaeNardetum strictae. The ecological differentiation of syntaxa is mainly based on certain environmental factors reflected in Didukh indicator values (DIV), management practices and altitude. Conclusions: This study complements current knowledge about mesic grasslands from poorly sampled area using the Braun-Blanquet approach. The classified syntaxa of mesic grasslands are discussed with respect to their distribution in the Carpathians and Europe and we expect that the results of our research will assist in the anticipated future supranational classification of mesic grasslands in the Carpathians.