The objective of the study was to assess the changes in vegetation and turf cover of psammophilous grasslands in the Kózki Nature Reserve under grazing and non-grazing conditions. The investigations were conducted in the years 2010-2013 in southern part of the Kózki Nature Reserve, in the Podlaski Przełom Bugu (the Podlasie Bug Gorge) Landscape Park where sheep of the native breed Świniarka graze as part of the agrienvironmental project “Preservation of endangered genetic animal resources in agriculture”. The pasture area is a mosaic of sandy grasslands of the Koelerio glaucae-Corynephoretea canescentis class and meadow communities of the Molinio-Arrhenatheretea class. The turf cover of the study areas varied depending on the type of phytocoenoses and on grazing the sward by sheep or the cessation of its use. Significantly greatest turf cover was determined for communities with species ChAll. Vicio lathyroidis-Potentillion argenteae involving species ChCl. Molinio-Arrhenatheretea and dominated by species ChCl. Koelerio glaucae-Corynephoretea canescentis involving species ChCl. Molinio-Arrhenatheretea, community with Calamagrostis epigejos and with Poa pratensis. Significantly smallest turf cover was observed for the Spergulo-Corynephoretum association where grazing by the Świniarka sheep led to successive reduction of the vegetation cover in the study period. Monitoring of the number of trees and shrubs indicated that all species of this group of plants, up to the height of 100 cm, were nibbled or damaged by sheep during the grazing. Therefore, sheep of the Świniarka breed can be used in the protection of psammophilous grasslands because they hinder the secondary succession of tree and shrub vegetation.